Definitely don't agree with actually challenging someone when you don't know the full story (esp since many on here have pointed out circumstances that would not be immediately obvious).
But I also don't like the way so many people take such delight in explaining (erroneously, surely?) that there's absolutely nothing anyone can do about non-parents parking in those spaces, with the obvious implication that they will and do take full advantage of this, and to hell with everyone else. Surely if you behave like an arsehole (by wilfully abusing the facilities) then the supermarket can ask you to leave? Sainsbury's have big signs threatening to fine people who park in p&c spaces if they don't actually have a child under 12 with them. Perhaps that's bullshit, but they still have security who could move you on. They're not compelled to be dictated to by the sort of people who think that anything that's not actually illegal is 100% fine, are they?
As I said, I don't agree with the OP's stance, but I do wish we didn't have to have this wildly polarised argument, where, as soon as you express the mild opinion that p&c spaces should really (according to politeness, not law) be for, umm, parents, suddenly you're a special snowflake who needs psychiatric help to manage life.
Yeah, sure, there were no p&c spaces a few years back. So? Does that mean they can never exist and be managed with consideration? It's a bit like saying that, because the nice new park wasn't there when your kids were little, it's now ok for your teens to sit on the swings all day drinking coke while the little kids wait fruitlessly for their turn.
Obviously p&c spaces need to be managed with common sense and politeness. OP didn't manage this. Neither have the 'back in my day' brigade on this thread.