Well nobody is holding a gun to your head to make you purchase anything, but if devs sell things for RetroArch, who cares? Don't buy it, and it won't affect you.
Unfortunately, that's the sort of attitude that tends to poison the well of good will that are emulator writers. So, even if I don't contribute to questionable activities, other people who do can still indirectly effect the future progress of emulators which does effect me. There's already a lot of drama around Retroarch as its gained a lot of focus while the emulator writers themselves are ignored. And the funny part, of course, is that people complain about Retroarch over the same reason they avoid the source emulator--relatively terrible, in their opinion, frontends. :/
I think Retroarch is valuable. I think the emulator developers themselves make something valuable. And I think that something like Retroarch would be a good thing to have on Steam so IP holders could sell ROMs and end the quasi-blockade* that is "roms are piracy"--aka 'mp3s are piracy". It's not that any of this is not a doable thing. It's just that reasonably it's better to play nice and ask permission, even when it's not needed, because the point of Retroarch shouldn't have been to just be a technological platform--which it is, and why it's so legally gray area on some things--as much as a collaboration platform. Honestly, at least for the moment it sounds like some effort is going that way, and I do hope it continues.
The way i see it is (and im wrong perhaps) they sell you a gun but no bullets, because guns with bullets are illegal but guns alone aren't, so its ok, they will find bullets elswhere....
Or selling an mp3 player without songs.. Seriously, Retroarch is for playing content. Some right holders have, directly or indirectly, sold the content digitally. Others are starting to rip their own collections. It's a chicken and egg thing, much like how digital music sales went where there was a lot of back and forth about how it couldn't possibly be people with massive CD collections wanting to consolidate their music nor would they ever want to buy more. The better analogy is wandering around in a desert and someone is provided cheap/free canteens, and the owner of the well refuses to sell you water because of course you'll just pirate it.
* Some IP holders already have, either in walled garden (Nintendo), one off consoles (often crap quality or legally dubious), or in relatively open compilations (with still often crap quality or legally dubious). Imagine if all your digital music was sold as albums each with its own bundled PC program to play it. It'd be a mess. :/