Freedom... It's a wonderful thing... and the best part is, you are free not to do stuff... you are also free to complain about said stuff, but we prefer if you just keep that to yourself.
One of the better things AHA helps to provide, thanks to your membership, is access to insurance to cover brew club events. It's not glamourous, it doesn't help you brew better beer, but it definitely would be expensive to acquire on your own, if you could at all, and many venues require it these days. If you are a member of a local club, in order to get the insurance (without having to pay a premium), a majority of members need to be AHA members. So, by having a membership, you are helping out your local club. I also find the quality of said clubs is better and tend not to be just a drunk-fest.
Laws also don't tend to be permanent. Although you can legally brew in all 50 states today, there is no guaranty that it will stay that way. You can be sure the big breweries and liquor store chains are working behind the scenes to lobby that privilege away, just as there are many groups lobbying to ban firearm rights. A lot of the stuff the AHA does is not visible to members, but it is vitally important. Luckily, our hobby doesn't have all the negativity around it that firearms do. If it did, and those lobbying groups chose to do a big campaign to blame drunk driving on AHA members, you can be sure it would be a lot harder to homebrew legally.