If society may be destabilized because one has the knowhow to create something of this scale but not the resources to properly moderate specific violent threats then perhaps a barrier-to-entry preventing that is a good thing
This is clearly retaliation for the H1-B caps / S230 threats of the outgoing administration, rather than corporate concern for the stability of the republic. How many people here can even say "corporate concern" with a straight face?
Business is war, alliances change. What they do to the MAGA grannies today might not be so amusing when the targets change.
Parler's userbase is comprised of people who were either banned or migrated away from Facebook and Twitter in protest of them cracking down on hate speech and systematic appeals to violent action.
They moved to Parker as Parker rather explicitly stated they would not act on hate speech and systematic appeals to violent action.