Don't think that flies. They quote a generic section on Termination for Convenience but completely leave out the relevant section on Suspension + Termination for Cause:
From section 6.1 on Suspension:
We may suspend your or any End User’s right to access or use any portion or all of the Service Offerings immediately upon notice to you if we determine ... (a) your or an End User’s use of the Service Offerings (i) poses a security risk to the Service Offerings or any third party
Then they go on to complain about how AWS has completely terminated them, but that section also doesn't appear favorable.
From section 7.2 on Termination:
We may also terminate this Agreement immediately upon notice to you (A) for cause if we have the right to suspend under Section 6
Parler has copious amounts of this violent content going back for months, so it seems like this is a sure case of a "willful and continuing failure" to apply the required moderation in the agreement. IMO this shows an ongoing breach of contract so the "for Cause" clauses would apply.
The Anti-Trust argument seems like the strongest here but that's pretty notoriously difficult to succeed with. I guess not too far from the App Store cases going on right now.
The AWS agreement is here: https://aws.amazon.com/agreement/
TLDR: Content promoting violence - clearly more than mere threats given the actions of several users on Jan. 6 - is against the AWS agreement and services can be terminated immediately upon notice.