It's not just Buchanan the cheap labor pimps despise, it's anyone who talks about controlling the borders. They have too much money invested in seeing to it that the slave labor pool doesn't dry up and so they're willing to steamroll their mothers if they get in their way.
Pat is also hated because he is for American interests only and because he is right about illegal immigration, trade deficits will lose jobs for America, homosexual practices and abortion are bad and foreign entanglements will bring war to our shores.
Pat is for the American interest war on al-Queda but against being the world's Globocop for the interests of England, Kosovo, Kuwait, South Korea, Israel, Taiwan or the Rock of Gibraltar. Of course, including Israel here makes him anti-Semitic and opposing homosexual practices makes him a homophobe.