Yep, there are no good choices here. Parler is an organizing venue for Trump supporters attempting to overturn a democratic election and/or storm the capitol, which also has a rather anti-democratic feel to it, no? So you can think of it as a trolley problem with "democracy" strapped to both sets of tracks. Since democracy will be a casualty, to one extent or another, in both the "do nothing" and "do something" options, the service providers must ask themselves: which scenario will hurt democracy worse?