For us, belonging to the AARP has been similar to the yrs DW belonged to a strong union with an active and powerful local. Like AARP, the union local sometimes negotiated for benefits that to me, observing as a citizen of the community, seemed far reaching, unreasonable, excessively expensive, unsustainable in the long run or just plain selfish (they grabbed because they could). Literature that arrived at the house in the mail was often so full of ridiculous propaganda, we couldn't get it to the trash fast enough. But.......... hey, the benefits obtained were landing right on our plate. And they were emmmm, emmmm good! So, despite it not being a closed shop, DW maintained membership (although was not active in any leadership role) and just accepted any "too good to be true" or "good for us but probably not good for the community" benefits with a shrug.
We do the same thing with AARP. My eyes roll back when I see some of what they're advocating. Yet, in aggregate, they seem to do more good than harm and at 62 yo I prefer to have someone looking out for my interests even if I disagree with some of the details.
Membership is so cheap that even thinking about cost as a consideration of belonging is silly. It's really a matter of whether you want them there or want them gone.