I don’t think character limits reduce spamming. Links can be replaced by tinyurls and instead of one 500-character-“BLABLABLABLA”-post, you can create two (copy-paste). The big downside is that serious discussion is also prevented (if you don’t want to have a paragraph for every sentence, which would cause your post to be interrupted by others posting simultaneously). As ultima ratio, there’s still the option to mute people.
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