If someone was off and pushing and/or obviously had a problem, I would stop. Thing is, you run the risk of implying they are an idiot, a numpty, who as said above, can't even put a chain on or who goes out unprepared.
I've taken offence when others have pounced on me, just because I've stopped and put my foot down, I often wonder if some of the over eager go out in the hope of 'rescuing' someone, to satisfy their crutch of cyclist superiority.
once, I was laid in the grass by the canal, enjoying the sunshine and a can of pop. This old boy rolls up, jumps off his bike, "right, what's the problem? puncture?, not brought any tools, eh?". "er...NO, I'm enjoying a can of pop, the sunshine and some peace and quiet!, (now **** off)".