In my experience in that context, it is more unlikely that "one" would be used by someone in conversation who is totally accepting of the situation being discussed. However you cannot draw too many conclusions from a short forum post. Some of my forum posts have been totally misconstrued as a result of a poorly chosen word or phrase!
If someone said "we have one of those in our family" then that would be much more likely to signify dehumanisation or non-acceptance, in my experience.