I can see some limitations might be a good thing, within reason. Prohibiting unwarranted or unsupportable claims in marketing could serve to bolster the credibility of the group. Getting too heavy handed with censorship of criticism of the group would be counterproductive.
I think there are enough brokers and agents out there who already begrudge NAR the dues they pay. Piss enough of them off and they just might take their listings elsewhere. It’s not like they don’t have or can’t come up with options.