Then you remove them all.
For free Speech purposes there are plenty of reasons to allow companies to choose who they do and do not want to do business with.But for free speech purposes, there is plenty of reasons to allow raw emotion on their platform such as the expressions of the desire to kill. It's healthy and good to express rage and anger. Venting is healthy.
Expressing the desire to kill someone is not covered by free speech and never has been.
Here's a thought experiment for you
If someone were to go on parler and "vent" about how much he wants to rape a child to death...would that be "healthy"?