1) The alt right has become so hateful that regardless of your approach to free speech that allowing it to propagate is unacceptable
2) Societies view of free speech has changed in the face of things like the alt right.
3) The expected role of sites like Reddit has changed as those platforms are used to spread hate speech, false news etc.
Whenever the admins make any changes, a certain sub-section of the site goes completely insane and spams the site with tons of threads about how the site is fucking terrible and how the admins are fucking idiots with the common thread among these rabblerousers being that they always happen to hate a particular group that is ruining the site and destroying the indomitable reddit free speech ethos.
Obviously that's not true, but major figures at the company have said it from the early days up through very recently. And the difference between moderation (in the "no spam, no personal threats, communities enforce their own rules" sense) and administrative speech restrictions is a big and challenging one.
So no, Reddit has never quite been that, but it's been one of their selling points regardless.
I think the biggest concern is when platforms start to police illegal speech, and countries make political dissent illegal.
But now that reddit has become something of a cultural focal point on the internet, it's started to draw attention from the media at large and suddenly the operators felt a little embarrassed that they had to defend subreddits such as /r/fatpeoplehate, /r/jailbat, /r/niggers etc. So I imagine they just said "fuck it, it's more trouble than it's worth", and despite a month or two of banhammer-whack-a-mole with fuck-stupid-dictator-sjw-cunt-ellen-mao subreddits, the site continued to flourish, and all the free-speech purists finally woke up to the startling truth that reddit.com was really just an internet startup and not a platform to empower the oppressed masses...
Until they banned another subreddit.
Except it's not that simple. There's a substantial amount of judicial precedent that you can't refuse service to customers just because you disagree with their ideology or background, otherwise it would be okay to refuse service to supporters of gay marriage for example.
It's appalling that you would even suggest that.
And as it states there, they also have censorship based on their terms of service, where they prohibit the posting of videos which violate copyrights or depict pornography, illegal acts, gratuitous violence, or hate speech.
Reddit isn't refusing to service people because of their ideology or background, they are limiting certain kinds of speech. A private organization is entirely allowed to limit certain kinds of speech.
Way overbroad interpretation. The Civil Rights Act prohibits refusal of some kinds of service based on race, color, religion or national origin, and it's pretty much the only national law (in the US) that's relevant here (I'm not counting the 14th amendment or more specific laws e.g. for disabilities).
Notably, there's no federal law protecting supporters of gay marriage. They're state-specific laws, and not at all universal.
Ideology isn't a protected class. Sexual orientation is, at least in some states.
Regardless, you are not refusing anyone service - you are not banning people from your platform, you are designating your platform as something not be used for certain purposes.
Who cares? The overwhelming majority of redditors subsist on photos of animals and drawings of video game characters. Just leave if reddit isn't friendly to your particular proclivities. If you hate fat people, liberals, feminists and BLM activists there are many places on the internet where you can find common cause.