I think there is also another side to this coin.
When I join a random crew I always start by saying hello and trying to help them straight away by repairing, bailing water and or grabbing supplies and I will say to them in chat "is it okay if I join your crew and that I will help in anyway I can?", but even then there have been a couple of occasions where I have joined a crew and immediately been thrown in the brig for no reason. I have been tempted once or twice to stay in the brig and take a share of their treasure but I find that too boring so I leave and try another crew.
There was even an occasion where a new random crew member joined my ship and started messing about, wasting supplies and stuff. When we locked him in the brig he complained, so we told him that he was brigged for misbehaving but if he behaves we will let him out shortly and he will get a share of our treasure no matter what. He didn't stay though.
I am not really bothered by the brig system as it is, even though it can be abused a bit. A means of kicking someone might be open to more abuse but at the same time it could also be put to good use to kick a random to make space for a team mate who is joining.
It's a bit of a "stuck between the devil and the deep blue sea" situation.