Self - appointed liberal moral "police" tend to be among the most irritating people out. The internet is like fuel for them, as they tend I guess to post disproportionately so as to make their own viewpoint seem the norm.
They usually lack the ability to construct a proper argument, remain neutral, take other people's viewpoints into account or research the issue properly. They will happily announce that "you can't say that" or "think that" without providing any kind of justification as to why, other than they say its offensive, or racist, or sexist, or whatever bandwagon they've jumped on. Except they forget that unless the law actually agrees with them and makes it illegal, they are wrong.
I often get the impression that those who most active in this do it as a kind of compensation for failure in their own lives, whether that be lack of career progress, relationship failure, lack of control in general. They will usually be very virulent in most, if not all of the following: the current government, Margaret Thatcher, supporting Scottish independence, conspiracy theories, Palestine, and so on.
Mumsnet is becoming particularly preachy and some of the things you read on here are cringeworthy. You are left thinking if they are that interested in the topic - do something useful, at least starting with getting a university education in the subject you are trying to preach upon.
But at least that's one relevant parallel with the worst of Muslim religions - they tend to be partly enforced by unqualified, self appointed preachers who interpret the Koran to their own ends.