Parler (and other services like it) has a contractual relationship with its users than enable it, and it's users, to conduct their business. You cannot just disrupt other people's business arrangements for any reason at all. Depending upon the circumstances, you open yourself up to claims of tortuous interference. I think there's an argument to be made here that this is exactly what Amazon, Apple, and Google all did.

Section 230 protections doesn't apply here either. It does protect against civil suits, but only for good faith attempts at removing illegal content. It's fair to question whether Parler has done a good enough job in that regard. If not, then the appropriate parties should sue Parler to force it to clean up it's act. But there is nothing inherently illegal about Parler, so there is no reason why these platforms deserve protection for thwarting the many perfectly legitimate users on the platform.