I think "welcoming them warmly at the door" is a helpful technique. Seems to me that the issue is not newcomers but lack of inculcation in the culture. If you want them inculcated, it helps to a) give them motive to get inculcated and b) give them opportunity to get inculcated.

Lots of online communities are really bad about being asshats to the newcomers (or just ignoring them like they don't exist). This is not a way to inculcate people with good manners. It is a good way to give them reason to be asshats back or, in the case of ignoring them, making them feel like they can do anything because no one cares or is paying attention to them anyway.