Yeah, the SCA can be a mixed bag. People come into it from a variety of different angles and different areas of interest. Some are closer to "living history", others are more casual. So you'll find people that don't care what you do, and will just enjoy having your participation. Others are very strict and will look down at you if you don't live up to their standards. It's like a microcosm of a society, with a broad spectrum of personalities.
When it comes to their combat system and knighthood, they have a very long and established history and way of doing things. Everyone has to play by their rules, since its the consistency that keeps the game safe. However, there are fighters in the SCA who keep pushing for change, because the combat culture has evolved into a "power = good" sort of mentality. I remember reading one account where a knight stopped fighting altogether after his opponent kept ignoring hits, until he finally hit the guy hard enough to knock him out.
While I'm a card-carrying member of the SCA, I only joined to get access to the newsletters, register my heraldry, and get my discount for attending Pennsic. While I'd love to take part in a larger organization like that, the combat system isn't as appealing to me, for the reasons I mentioned above. I prefer the HEMA/WMA community I've been participating in, learning historical weapon techniques in the context of a martial art.
To me, if I joined the SCA "heavy" fighters, I'd probably go in with the goal of being knighted, which would almost certainly not happen. In some ways it's more a popularity contest than anything else, since they base it on renown as much as prowess, and the decisions are made by the ruling king with recommendations from the existing knights (and the kings are chosen by right of combat too). Atlantia (our kingdom for this area) is notorious for turning out very few knights, if I remember correctly. The ones who tend to get knighted are those who don't have an outside life, and can devote 40 hours a week to the game. While chivalry factors in, it's not always at the forefront. And those who do get knighted usually take a good 10 years to get there. By then, many of them burn out and disappear from the combat scene after a while.
So personally, I'd rather take part in an Order or other small organization that's more focused on combat and chivalry specifically, with a clear path for advancement and/or membership, than be told that I can't portray a knight or wear a white belt because I'm not willing to knock people unconscious right through their helmet.