I find these things really depend.
If partner 2 is refusing because they "just aren't that into it" or "don't feel like it" then they're selfish and should suck it up and do it. If they don't, then partner 1 should leave them and find someone who enjoys what they enjoy.
If partner 2 is refusing because there's something about it that really turns them off or makes them uncomfortable and always will (I will never be into piss play, for example) then partner 1 needs to decide whether it's worth it. Compatibility is a big deal. If it's something that they will never feel fully sexual fulfilled without having in their sex life and your partner will never feel comfortable or good about doing it, then something has to give.
I'm totally of the opinion that you should TRY to please your partner, be up to new experiences, all that. Most of the time in popular culture, the one who wants more sex or sex of a different kind is the one presented as the bad guy. In many more sex-positive communities, an overcorrection occurs where the person who doesn't want to do other things is the bad guy. This simply isn't true and I think it can sometimes shame people for wanting to say no to things they don't enjoy and aren't comfortable with. Everyone should be able to say no and everyone should be able to ask for things they want.