1) No, I don't believe working class is primarily an identity (although it can be and should be that as well).I regard it as an objective social reality. One can be a member of the working class even though one does not identify with it, or even know he/she is in it. But far better to know and identify than not.
2) I regard the struggles of and for human beings as being inherently more important than those on behalf of plants or animals. While I'm against cruelty to animals I don't believe they are or can be possessed of rights. One must be a rational being, actuallly or potentially, to have rights. Call me an anthropo-chauvinist. I plead guilty!
3) No, I don't think the class struggle is one among many (for gender eqaulity, gay rights etc) I think it's more fundamental because I believe the expoitation of the working class by the capitalist class is the basis of our entire society, while special oppressions, though hideous, are not. One can be for the abolition of racial and sexual oppression without opposing capitalism. One can't be for the abolition of expoitation of the working class without doing so. I do think, however, that if the working class is ever to overcome capitalism, its struggle must embrace opposition to all froms of oppression and (human) inequality.
4) I don't think that respecting picket lines is irrational. It is based upon the reasoned belief that the way to a better society, or even the defense of the social advances we've made in this one, lies through the fight of workers against bosses, and that the most effective weapon in his fight is the collective action of workers. Ninety-nine percent of picket lines represent workers in conflict with their employers over bread-and-butter issues, and in such conflicts I don't have to inquire as to particulars. The workers are always right. Therefore, when I see a picket line, any picket line, the chances are that it's of this type, and honoring it takes the form of a reflex. If I later find out that it belongs to the other one percent of picket lines (for some political cause, maybe a rightist one) I can exit the reflexive mode, evaluate, and act accordingly.
I would be happy to argue for these propositions rather than merely state them. But it would take a lot of time to argue for each, and, besides, others have done it far better than I ever could--Marx, for one.