Even when dealing with people acting in an obviously dangerous or harmful way, I think it is worth treating them as if they were good people temporarily doing something wrong, either because of good intentions gone wrong or temporary insanity.
There are a lot of reasons for treating bad actors that way. One big one is that most people are very reactive. If you treat them in a way that they perceive as friendly, sympathetic, and respectful, they are much more likely to respond in kind. Another reason is that a lot of people like fighting: if you don't fight with them, they'll eventually go find somebody else to scrap with.
That's why we only use bans as a last resort. If it has reached the point of someone being banned then it means treating them in such a manner has failed and we've had to resort to stronger methods. Assuming good faith for people that have had a little trouble in the past (a handful of short blocks, perhaps) is a good thing, but if they've been indefinitely banned, then they've already had every second chance they deserve.