That some people post threats in violation of policy is not at all unique to Parler. Twitter has had a longstanding and pervasive problem with threatening conduct and threats, so much so that Amnesty International calls it Toxic Twitter, and wrote reports on violent language directed at women on Twitter, and Twitter’s failure to remove death threats. Not that long ago Twitter hosted accounts for the military wing of Hamas, and related entities (I know, I used to check the accounts when something was happening in Gaza).
If you have spent any time on Twitter, and I’ve spent a lot, it is a cesspool of hate and conspiracy theories, particularly related to so-called Russia Collusion. The notion that Parler is worse is a fabrication.