Unethical? Definitely not.
Site participants know it’s done; nobody is being fooled or tricked.
It is done in an “all in good fun” spirit, and occasionally to warn people that a particular poster is a troll.
On a personal level, it doesn’t bother me.
The only issue I can see is if an individual doesn’t like and/or is embarrassed by a subtitle, in which case the should probably be accommodated if they request a change.
JMO