That often comes down to what someone thinks is spamming. While much spam meets the Justice Potter Stewart standard (I know it when I see it), I’ve seen Akismet flag posts that were perfectly acceptable for no discernible reason. I’ve also been a part of communities where almost anything off-topic, especially if it has a ‘commercial’ feel to it, is considered spam even if Akismet lets it through.
And I’ve had more than a few users who got hacked and were being used as a spam conduit without their knowledge.
So in any given community, there may be mitigating circumstances surrounding labeling someone a spammer, especially if it involves taking actions that are not easily reversed or without any type of due process.
And sometimes what’s really needed is explaining to the ‘spammer’ what is and what is not acceptable. I’ve found most people will pay attention to a reasonable explanation of a community’s standards, though there are people who just want to be troublemakers or don’t believe rules should apply to them.