I don't think reddit is the measure of acceptable discourse. If the_donald was banned it would just mean that its users would have to find another subreddit or site to use, it says nothing about what type of discourse is generally acceptable. Further, I think it's pretty obvious by now that reddit's problem with the_donald is not related to their political ideas since there other subreddits supportive of the president that have had no conflicts with the site admins (e.g. /r/conservative, /r/republican).
That's the problem though. The mods were repeatedly hostile to any attempts by the admins to handle the more egregious rule violations. The admins have treated them with kid gloves for years now. They were historically one of the worst sources of brigading of other (much smaller) subs. For instance, /r/legaladvice had huge problems with them in the past.
Even the chapo mods complied with the admins when they were asked to crack down on calls for violence... Even though those calls for violence were about _dead_ slave owners... Hard to kill someone already dead.
Of course I am not referring to the worst stuff on that subreddit, there is shit there, and much more than average, but if a sizeable part of the population has views like this is banning it really fair? I worry that banning public speech by a large segment of the population fractures the population that makes things even worse. And once fully separate it leads to even more echo chambering and divergent realities and more problems, not less.
But again that is assuming it is genuine and not trolls or foreign interference and it is truly sizable and not fringe.