The contrast here is between two comparisons:
- The US vs. an ideal US that progressives would like to exist, which won’t have any racism, sexism, homophobia, etc. The US is indeed inferior to an ideal that may or may not be possible.
- The US vs. the countries of origin for illegal immigrants (Mexico, El Salvador, etc.). The US can ace this comparison easily. Just ask Manuel Labor who prefers to live in the US under constant threat of deportation rather than in his poor village in Mexico.
It is no contradiction to say that the US is better than Mexico, but not as good as it could be.
I think that there is a contradiction between wanting to fix US culture on one hand, and encouraging immigration from places where the problem that needs to be fixed is even worse. If you really want a less sexist and homophobic US, having more immigrants from Mexico is probably counterproductive. But that is a separate matter than the meme.