In Swift's "A Modest Proposal," the speaker's allegiances certainly lie with the Irish poor. He is speaking with irony when he says all of the nasty things he says about the poor.
Specifically, he mimics the English view of Irish people. He imitates their bigotry and prejudice.
He certainly degrades the Irish poor if you take what he says literally. But he goes so far overboard, that once the speaker reveals what his proposal actually is--use poor Irish children for food to alleviate poverty--the reader understands that he is being ironic.
Concerning the second part of your question, the speaker doesn't really identify himself as part of any particular social group. That's not relevant. He certainly identifies himself with the Irish poor, however.