Obviously an emotive topic but don't for a second think this topic is anything to do with the health risks, because if that was the case HigherFlyer would be equally upset about people sneezing on the plane they travelled in.
So try to get this in perspective and realise that it's all about sensibilities - and some people, like HigherFlyer, are clearly not impressed with seeing a naked and dirty butt in the seat next to them. Equally some parents would never consider changing their baby in front of complete strangers because they realise that, right or wrong, some people DO find it offensive.
I'd be quite happy to have neither the particular mother who the question was first asked about nor HigherFlyer sitting next to me . . .