The NRA was founded in 1871, to promote marksmanship, and safety. And that's nearly all they did for nearly 100 years.
The NRA didn't enter the policital area until the realized they had to (there was no one else) in the later 1960s. They created the ILA (Institute for Legislative Action) as a separate organization to comply with the laws and deal with political issues.
I think if you own a gun, for any reason, you ought to belong to the NRA. For the insurance they provide as part of the membership, if for no other reason.
Membership at a certain level gets you a vote for the directors. If you don't like a particular position they take, you can vote them out. Kind of like our govt in that way, in theory, at least.
Won't say that everything they've done in recent decades has been the best possible course, but nobody else has the clout (or is so demonized), so they must be doing something right.