The consideration of political principles can seem dry and abstract, but a more explicit awareness of one's principles can foster more effective political influence.
One of the advantages of being progressive is there is no need to be un-principled -- no need for deceit, obfuscation, or opportunism when one aspires to the greater good. To be unprincipled, or even just inattentive to principles, is counter-productive when one seeks to inform and encourage rather than misinform and manipulate; it only brings one's clarity and motives under suspicion.
A political principle is a guide to forming opinions and taking action. To be politically principled is to aspire to consistency, to avoid hypocrisy, and ideally, to find the most ethical and/or moral way of interpreting and reacting to issues and events. To be politically unprincipled is to argue or act in the interest of one's ulterior motives or occasional goals by employing a deliberate distortion of principle, or disingenuously denying its relevance to a situation. To be unprincipled can also be unintentional -- an expression of bias, confusion, or carelessness -- but these at least are more easily improved.
Principles are not pure and simple in actual practice. It's not always appreciated or acknowledged that a principle will have legitimate exceptions and limitations. A principle such as "to kill another person is wrong" can be modified with "except in self-defense, or in defense of a helpless victim, when less extreme means are impractical or unavailable." There can be disagreement over whether an exception applies in a particular case, but it's only a principled disagreement if the basic principle is acknowledged along with the possibility of reasonable exception. To argue that killing is always wrong no matter what, just to counter an opposing view toward a particular situation, would be an unprincipled way of trying to gain a rhetorical advantage, as would trying to justify a murder as having been in self-defense when it obviously wasn't.
A principle can apply to inter-group or international relations as well as personal interactions. The difference is only a matter of scale. "To kill is wrong" can be expanded to the national level with "except when a nation is invaded by another" and in that context, "except when a person is defending his or her nation from invasion." The contention that national principles are different from, and somehow above personal morality, only serves to justify international misbehavior.
Principles can be relatively inclusive or exclusive. An extremely exclusive principle would be "killing is wrong, unless the killer is American and the victim is not." It's arguable that the difference between a progressive principle and one that is conservative is its relative inclusiveness -- the size of its "we-circle." To be progressive, I believe, is to aspire to progress toward the eventual dissolution of tribal, regional, national, racial, gender-based, and religious antagonisms; to be conservative is to favor the conservation of some form of exclusiveness and privilege. However distasteful, both can be principled in their own way, the only difference being their relative inclusiveness.
The implementation of principles can be relatively practical or impractical. Prohibitions against the violation of a principle may sometimes be beyond reasonable remedy. A murderer who escapes into a wilderness and eludes capture for an extended period of time may render the principle that murder must be punished impractical. But the decision to abandon a principle due to impracticality in one case can't (in principle) be used as an excuse for inaction in another.
False principles can be shown to be baseless and indefensible by reasoned argument. The commonly alleged principle that the US is a Christian nation, and subject to the dictates of Christian authority, is indefensible against the objection that the Constitution established freedom of religion as a supreme law of the land. That allegation can never be sustained in a principled way, only defended by evasive and elusive argumentation. To be principled is therefore to be alert to finding oneself evading a direct argument over principle; it indicates that the alleged principle being defended is likely in need of reconsideration, if not modification or complete abandonment.
There are principles that might actually be called anti-principles, because they are used opportunistically, simply to try to obstruct genuine principles. When abolitionists sought to establish the principle that slavery is wrong and should be made illegal, an anti-principle was used to claim abolition could or would never happen, and that to call for its abolition was unrealistic. An anti-principle is a simple and abstract claim of natural fact that some condition, right or wrong, can never change, regardless of principle.
An absolute commandment might claim supremacy over principle, as when a person's religion proclaims that killing is a sin without exception. Pacifism might be considered justifiable as a commandment, but by its absolutism it is outside real-world personal and political realms, and is neither defensible nor reprovable as a political principle. To believe that it is better to be murdered or tolerate a murder rather than use whatever force is necessary to frustrate a would-be murderer or foreign invader is to invoke an ideal world with transcendent values that render actual personal and political considerations irrelevant.
Some principles are relatively abstract, and implicit, but fundamental to more practical principles. The basic principle that one's political positions should be free of unjust or unreasonable bias can be inadvertently overlooked when considering issues with important and urgent implications, especially those that are emotionally charged. But if one aspires to take positions that are ethically or morally principled, the fundamental problem of bias will be earnestly and conscientiously struggled against.
International humanitarian intervention
My motive in writing all this is not to weave abstractions. As the title indicates, my ultimate focus here is on the issue of international humanitarian intervention. I believe a principle that states something like "it is sometimes necessary and right for the international community to intervene in a nation to prevent genocide or massive injustice toward some part of its population" can be justified, with legitimate exceptions and qualifications. But the positions taken by many in the progressive community have not been sufficiently clear and reasonable in reaction to some recent international crises. It is my hope that an explicit consideration of political principles can resolve some dissension and help consolidate more influential and effective positions and actions in the future.
If pacifism or an anti-war creed are considered absolute commandments, they are not pertinent to the issue of armed humanitarian intervention. An anti-war principle is not a position that would be maintained in all situations, so it should always be supplemented by specific objections, and open to the distinction between a war of conquest and a legitimate humanitarian intervention. To object to a military intervention as-if in principle with an unequivocal anti-war argument, and then on another occasion support the militance of one side in a conflict, would be hypocritical. Even if the day hasn't yet arrived when an anti-war activist is compelled to support a military intervention to stop a campaign of genocide, to be simply "anti-war" is to look naïve, idealistic, factional, and/or extreme to someone who might otherwise be receptive to an argument against a particular intervention. A principled objection to an intervention (not anti-war but anti-this-intervention) would have to be framed "because of x", where "x" consists of exceptions to the principle.