In court there’s a concept called “falsus in uno, falsus in omnibus”[1]. If you’re shown to have lied to the court once, then anything else you’ve said can be considered to be a lie as well. You lose the assumption of good faith of the judge and jury.
It might not be a courtroom, but the same concept applies to a so called “bastion of free speech” platform like Reddit.
[1]: https://en.wikipedia.org/wiki/Falsus_in_uno,_falsus_in_omnib...