I was on Parler for several months, trawling it and other sources quite heavily for the last month or so, trying to keep abreast of ... events.
At no time did I see even a single post advocating violent overthrow of the government, white supremacy, etc. Apparently, neither did any of those planning the Capital attack, since they were not Parler members.
So, if you want to deplatform people based on their political leanings, I guess you can go ahead and do that. But, the "reasons" being used to shut down Parler don't seem to be founded in fact.