The problem of sub 50 rep users being unable to comment is well documented
The rationale for the 50 rep limit is good: reduce spam
As evidenced by many of the answers to those questions, the problem that this limit is trying to solve is that of spam.
The justification is simple: we don't want the site to be flooded by comments from passers-by. ЯegDwight
The canonical answer to this question is found [here](https://meta.stackexc