I saw a comment on an answer on SO that was made by the answerer. The comment was "if useful +1". I flagged it for removal and it got removed about a minute later. Can we prevent such useless comments by blacklisting short "+1" comments?
Blacklisting specific words from posts or comments to a point where they can not be posted or will be automatically deleted after posting will only 'move the problem', people will only get more creative in their ways to still post their one-up comments.*
A system-level blacklist will only make people write more creative comments trying to circumvent it. There's no easy fix for this, people will also abuse comments to make remarks like 'good answer', 'I agree'...
Any comment that's not doing what comments are for (request clarification, leave constructive criticism for improving the post, add relevant but minor/transient information) can be flagged as 'no longer needed'. It is suspected that short +1 comments already require less of those flags to be deleted, which will help a little in keeping at least those comments under control.
Blacklisting '+1' entirely will probably get a few false positives, e.g. when mathematical formulas are involved, and some creative (but barely legible) ways to still circumvent not being able to post 'pl0s 0n3'. So, it's probably better to not let the system prevent or automatically delete them, but have some human oversight. Just enjoy your helpful comment flag count going up :)
* I seem to remember a meta post on how people would replace characters when words are blacklisted somewhere already but I can't find it