I wouldn't go back.
If I were to go back and not say anything then I am almost complicit in what they're saying. It's like passive support. I'd hate anyone thinking I agreed with that vile crap.
At the time I would probably respectfully ask them not to say things like that again as I find it offensive. I've done that before. What do they say all it takes is a few good people to stand by...
DH and I have very close friends who are gay and I have heard awful stories of them getting abused in public by homophobes. One of our dear friends (a 50 year old woman) keeps her 10 year relationship secret in her workplace due to homophobic attitudes.
I could never on my conscience knowingly associate with people like that as I would feel so disrespectful to my friends