>>96697830
Roleplaying is often a way for people to show their true selves.
A good DM should allow PCs to do what they want within reasonable expectations of the setting.
However, this should always have conquences. If PCs want to be murderhobos and villains, so be it. But then they should have to deal with actual heroes or anti-heroes trying to kill them in revenge.

A good example of this is what happens in the Westworld tv series with the character in pic related.