As a member of a minority group, this statement is sadly something we hear all the time if we object to people asking what should rationally otherwise be considered highly inappropriate questions. For example, just because someone is highly open about their sex life doesn't make asking a lesbian completely out of context how she has sex any more appropriate.
"Well, I would find it useful and be thankful"
Anyone who is a wheelchair user or has friends and family who are will probably know this one. People (strangers) have a habit of pushing wheelchairs around without asking the person within the chair first. Just because a currently abled body person might find the idea of someone helping them personally by pushing their chair if they used one, doesn't make it any more acceptable to completely ignore the wishes of a wheelchair user they don't know.