Almost everything on Parler and similar sites that is
not explicit calls to violence against specific targets and does not call describe black people using the n-word and does not talk about things like how the Nazis were right when it comes to Jews could be posted on Reddit in /r/conservative without violating any rules of the subreddit or of Reddit itself.
Most of it could also be posted on Twitter and Facebook, although there it might get labeled as misinformation.
It's actually fairly difficult for the overwhelming majority of people to get legitimately kicked off of most mainstream social media. By "legitimately" I mean by actually violating the site's published rules. At the scale of these sites there are occasional mistakes made where someone gets banned who shouldn't, and it can be difficult to get that reviewed, but nevertheless for most people those sites are "free speech social networks".
Because of this, when you start a site like Parler you get almost all of your initial membership from those people who got kicked off of Reddit, Twitter, etc., or who are having to work at not getting kicked off because they want to post calls to violence, etc.
That sets the tone for the site from then on. Hence, when a site is specifically selling itself as a "free speech social network" it almost always can correctly be interpreted as "a social network for extremists who could not follow basic norms for civilized discourse" for some X.