To me its strange someone would consider closing down /pol/ a "slippery slope". I am amazed that someone would consider 4chan a moral compass for the type of things their admins should put up with. moot has closed down /pol/ for this very reason in the past with even less "political" awareness than the CEO of cloudflare.
4Chan is "free-speech" not through effort but through negligence & apathy. moot shut down /pol/ (aka /n/) before, twice, on a whim because he didn't like the content. It's not the first time it has devolved into nazi-fetishism. While 4chan has the reputation for being a seedy place, moot has taken stands and banned people and conversions from 4chan (for example most recently gamergate on /v/) for reasons that can be boiled down to that he didn't like it (mods of 4chan have done this as well, such as no Naruto on /a/). The current iteration of /pol/ has likely been allowed to live through negligence - moot is no longer involved with 4chan, and the new owner hiroyuki has been as absent as moot during his VC startup days. Simply put 4chan never had any moderator accountability (see Rule 9 of the internet).
In conclusion, the notion that this is a "slippery slope" is nonsense. "Free speech" on the internet never really existed, the current view points that exist only exist because their operators have never bothered to flex their muscles - and the reason they haven't has rarely been because of some moral high ground. At the end of the day there is plenty of "reasonable" content YouTube won't host for you, and that Facebook will kick you for. If you are concerned about being silenced by a corporate vendor, then choose your partners wisely. If none will support you - then self fund. Free Speech doesn't mean the NYT is obligated to print your content, only that the government wont stop circulation of your newspaper. If you can't acquire the resources to start your own print, then tough luck.