Another hidden assumption here is that America has, in fact, withdrawn from the world. That hidden assumption is blatantly false, as those who engineered the February coup in Kiev are well aware. Close American involvement in the unconstitutional overthrow of an elected, Russian-leaning government and its replacement with a Western-leaning junta is a reality that rather blurs the picture of exceptional American purity and persistent Russian perfidy.
So one partial answer to the question would correctly be: I don't "fight the perspective that America withdraws from the world," because that perspective is disconnected from reality. A more expansive answer might mention that the "perspective" is a rightwing talking point that would lead logically to the experience of Iraq-in-Ukraine, only much messier.
Rhetorically, one might add: "withdraws from the world"? Really? You mean the "pivot to Asia," maybe? Or are you referring to the thousand or so U.S. military bases in countries that may have missed our "withdrawal" (Okinawa has perhaps a majority population that would rejoice at any "withdrawal")? Or maybe you're relying on the "need" to contain all those five Russian overseas military bases (in Armenia, Syria, Tajikistan, Kyrggystan, and Transnistria)?
The assumption that there is such a perspective of American withdrawal hides yet another assumption, that any American "withdrawal" from the world would, in and of itself, be a Bad Thing. And that hidden assumption hides yet another: that American imperialism is unquestionably a Good Thing.
Sometimes the invisible hides the imaginary, sometimes the opposite
And then there's the second half of the question, the assumption that America "is no longer feared by his [sic] opponents." Again, no evidence is offered or implied for this assumption, which is another New American Century-type rightwing talking point. A more realistic assumption would be that America is feared by everyone to a greater or lesser degree, whether for some act of active destruction (see list above) or some passive act of destruction (such as inaction on climate change that leaves island nations to the mercy of rising sea level).
Another hidden assumption here is that "fear" is a desirable basis for an international relationship, especially with one's "opponents." Since fear is a basic tool of the bully, the further assumption here is that it's good for America to bully any part of the world that opposes it. Fear is also the tool of the colonizer, the slave master, the imperialist, the aggressor. Fear is a tool of direct attack on the sovereignty of others, and opens the way to attacks on their territorial integrity. Fear has its uses, to be sure, and can be effective sometimes, but is it a default value of peacemaking statecraft seeking a stable world of interdependence?
As the United States proceeds with its military build-up in the Baltic countries, in Poland, and in other places proximate to Russia, is there anyone who should not be afraid? Is there anyone who does not understand that advancing US/NATO forces, by definition, bring the threat of tactical nuclear weapons that much closer to Moscow, which has tactical nuclear weapons of its own?