But what's the point of a -rep system if admins just ban you? O_O
We don't ban people based on reputation, we ban people for bad or anti-social behaviour, and only in cases where the offending behaviour is repeated after warnings have been issued or for particularly bad offences. It just so happens that banned users often happen to have a low reputation because the community objects to the same behaviour we have warned and banned them for.
Unless you do something really bad (posting porn or signing up just to spam might be examples) you would usually receive several warnings, and perhaps be temporarily suspended once or more before we resort to a ban.
To provide a concrete example, the aforementioned BB1995 was unofficially warned (that is, told in-topic to behave, but no official warning was recorded) a number of times, given 4 official warnings, temporarily suspended for 7 days once, and was
then banned. They were trolling with pointless and/or simple-to-answer topics in which they then complained about the legitimate responses they were given and/or simply ignored the replies, and were abusive to other members and/or staff a number of times. The low reputation is a result of the community objecting the this behaviour, and is independent of the user being banned.