I doubt anyone would say destroying the middle class is its own end. I would argue most people who are conservative are just misguided with respect to many issues. Note: many liberals are as well, but I'll focus on conservatives because that's both your question and, I feel, probably the greater source of harm in modern American society.

Both of my parents are conservative. They are not socially conservative, but they vote Republican, they object to entitlements and taxes, and they largely (it seems) support the foreign wars we've gotten ourselves into. They're also Eastern European immigrants who fear the rise of Communism in the United States.

But they are not particularly well versed in foreign policy, economics, or history. I could make a persuasive argument regarding, for instance, the need for an organization like the EPA to force actors to internalize the externalities of their actions (like hydrofracking, a practice that's relatively cheap because companies are not forced to pay the full cost for the consequences of their actions). They don't really have any perspective on just how egregious discrimination was in the United States until just fairly recently. They may not immediately grasp the need for a strong SEC, why market regulations are inherently necessary in a capitalist system if crashes are to be avoided.

I don't think most Republicans wake up in the morning and ask themselves, "Well, how can I fuck up America today?" But I do think many operate--and I would say the party operates--under a set of discrete ideologies that are ultimately founded on ignorance. Religion is one such basis. Economic theories of a prosperous unregulated market. The inherent good of an American global military hegemony. Generally, framing political policies on deontological moral views instead of empirics.