A parser, especially when built-in, can result in a experience where players feel judged. It's a similar feeling that keeps certain players from picking up the tanking/healing role, so making DPS less comfortable to these players can result in them leaving the game. On the other hand, if a built-in parser is present, and is limited to work only in pre-made parties (if the leader enables it) or solo, I don't think it's too much of an issue.