4) "The suffering which those and other similarly extremist policies and attitudes will impose on marginalised and already oppressed populations has a high probability of being significantly greater than that which will result from a Clinton Presidency."
The reverse could (and is) argued and this therefore is no more than personal opinion. In the absence of a discussion of Clinton's political direction (war being of especial concern to many of her detractors on the left) there is little or nothing to support the justifiability of this statement. Furthermore, if we are minded to accept Chomsky's own ethical basis concerning the notion of consequences, we may point to the longer term risks of accepting LEV: that of perpetuating a system which ultimately may do more substantive damage than a short term adverse Presidency. However, we should not accept this as an argument either, if we are to be scrupulous in our consistency, because both are wrong.
5) "4) should constitute sufficient basis to voting for Clinton where a vote is potentially consequential ie. in a "swing State." In view of the previous statements' being wrong and improperly advanced it is impossible to accept this which is directly consequent on the former. It assumes that 1)-4) are sound, which they are not.
6) "The left should recognise that should Trump win based on its failure to support Clinton...it lacks concern."
This simply does not follow: it may be argued that it shows political opportunism rather than sound principle. It is more of an election slogan and the argument of the political bully: eg. Brexit:"Vote to stay in EU or we will all be poor and ruined." Hitler: "Vote for Nazis or we will be taken over by Communists." Neither are sound or logical arguments, but rather arguments designed to persuade. "Do this or else this" is a variety of logical fallacy of the veiled threat, ad baculum variety.