Definitely not. The only comments that are hidden by default are the [dead] ones, and anyone can see them by turning 'showdead' on in their profile. Outright deletion is possible, but only for a few hours, or if the author specifically asks us to later. There have been a handful of exceptions in obscure cases over the years, mostly for legal reasons.

Btw, for anyone who has trouble reading a faded comment, you can click on its timestamp to go to its page and the text should be readable.