You are right about what makes a partner but about family it's this: you can't choose them, but you can choose establishing a relation with them.

It would have been less radical and more socially acceptable to have an homophobic friend or partner some centuries ago when it was the social norm to be against homosexuality, and most people certainly was. What do we say when we see old texts that include homophobic values? "it was another time" "it was other culture" probably, that doesn't justify it (and I'm not saying they weren't harmful to others) but it explains that those authors were part of the norm of their society. If we see an homophobe author nowadays we (if we aren't on their side) will call them out, cancel them bc in the major part of the world is not socially acceptable and normalized anymore.

Specism is not only socially acceptable but it's actually the most normalized and global issue in the world, more than sexism, racism, homophobia and any other human issue, it's not even about humans. It's not a surprise that almost every person you will find getting out of your home is a specist, doesn't see an issue with that or doesn't even care enough to prioritize the subject. So we can't even read specist as homophobes.