I can see how it can be offensive and I would have gotten offended when I was young. Now, around age 30, I would be perfectly fine with someone asking that. I would explain in more detailed terms, "I wish!" I liken it to asking a bride/groom "Are you sure you want to do this?" before they get married. It's a risky ask, but I feel someone should always that difficult question. We cannot begin to understand a nuanced dynamic between mother and child or any two close people for that matter. Possibly the mother was frustrated and lashed out? I have an older brother who can barely listen to my stutter. It frustrates the shit out of him. I don't blame him for being impatient, when it is MY stutter that's literally wasting his time. I just don't hang around him often. Also, I would bet that a small percentage of people who stutter would NOT give it up if they had the opportunity. For some, it gives them an identity that they may want to keep. Maybe the mom was asking something like that?