I think that the discussion about use of language is a small part of a much more important issue.
MN has a massive cross-section of (mainly female) society. There are people on here with all sorts of situations and backgrounds, so as a user you are exposed to life experiences that are often far removed from what you experience in your own life. A lot of us have relatively narrow social circles - in that we have friends and family who are in similar financial brackets, working in similar sorts of jobs, with fairly similar outlook on many things.
On MN you get a chance to hear about things from points of view that you would never normally be exposed to. For example, we have a couple of friends with children with autism, but they are not people we see regularly and I therefore know relatively little about their day to day lives. I don't know anyone with a child with a serious physical disability, although I was in and out of a wheelchair myself as a child. The reality of living with a disabled child or one with special needs is therefore something that I would know little about were it not for MN.
Having been exposed to different ideas and situations it would be rank arrogance for me to continue to assume that my outlook on life is adopted by everyone else in the world. I think I have pretty mainstream views - I don't consider myself a thoughtless person and I value things like courtesy, kindness, a work ethic, honesty etc. So I would imagine my outlook overlaps with that of many other people - but I don't assume it is identical. MN really brings that home to me. I often see people take offence at something that would not have particularly occurred to me as offensive. Sometimes I think they are being silly or deliberately confrontational, but more often I read a bit more about their circumstances, or simply think about what they are saying, and realise that there is a good reason for their stance.
I have my own personal views on what is an is not acceptable - everyone does - but being part of a community like MN is, for me, about being flexible in how you assert those views. Offensiveness is not solely determined by the user of a particular word - it is dependant on context and on who the listener is. There is nothing wrong with thinking "well, I think you are being a bit over-sensitive" but still moderating your use of language in accordance with what people around you are saying about it. You don't have to be all wishy-washy and just say what people want to hear, but equally there is no need to aggressively assert your right to free speech at the expense of others' sensibilities.
Language grows and changes all the time, as does society. It is quite possible that a few years down the line some of these terms that have been discussed will have lost their connection with their offensive roots. I also think that the more inclusive we become as a society, the less these arguments will arise. If people with learning disabilities are seen as full and valuable members of society, the occasional use of an old-fashioned offensive term is likely to attract less censure as there simply won't be the need for such robust rooting-out of potential prejudice. People will be more inclined to accept that it was just a slip-up by someone not thinking.