Hint: this is a good sign you aren't.
"I'm all for freedom of speech, but that obscene material just has to go."
"I'm all for freedom of speech, but that blasphemous material just has to go."
"I'm all for freedom of speech, but that sexist material just has to go."
Your examples don't apply. It would be more akin to:
"I'm all for freedom of speech, why can't I shout racist expletives at black strangers in the street?"
"I'm all for freedom of speech, why can't I send people abusive messages online?"
"I'm all for freedom of speech, I should be allowed to take photos of people going about their daily business, then encourage a bunch of my friends to be abusive towards that person."
Do you think it is ok to walk down the street and shout abuse at people? If not, then why it is ok online? Or is it only ok when thousands of people shout abuse at one individual rather than one on one abuse?
What right of others' does that infringe?
In general I recommend Ken White's writings on hate speech and the 1st amendment: http://popehat.com/2015/05/19/how-to-spot-and-critique-censo...
But anyway, none of this of course applies to the reddit example since reddit is a private entity which can do as it sees fit.
I don't care how you feel about obese people, this type of thing is unacceptable. I don't care what justification you use (race, sexual orientation, dress style, hair color, etc) it is unacceptable across the board. You don't have to be fat to see that this is wrong, you just need to have basic empathy.
PS - I've spent a LOT less time on Reddit as a direct result of how toxic the community has become. Hopefully this will roll that back if just temporarily.