It's a big Internet - there are plenty of places you can go and air your views. Or you can create your own site. Meanwhile, reddit has apparently decided they are serving the market of people who want to discuss the subject without the interjections of those who disagree.
Freedom of speech is a property right - you have the right to use your own press, your own soapbox, etc. Nobody's obligated to provide one. And some people just want to be left alone in private. If they do, of course, the rest of us are free to point them out just in case anyone wants to avoid that group. Maybe that's all you were doing here.
That is perfectly fine. I agree. Reddit is private. Not sure about the second part: "...Why dont all newspapers do the same?". The intention is to make sure there will be no places for "non believers" to express there views beyond reddit, and that is the real message there. Only vetted places should be allowed to filter for people who agree with each other.