Unlike conventional superheroes such as Superman, who stood for justice, fairness and decency, the modern macho superheroes portray a negative masculinity, characterised by mindless aggression and rampant sexism. Lamb, who surveyed 674 boys aged four to 18, claimed these hardnosed heroes may be damaging the social skills of teenagers and even affecting their performance at school.
It's curious that the objection isn't that superheroes glorify vigilantism, which you would expect to be the main objection. Instead the doctor's objection is that today's superheroes are macho jerks. It's certainly true that you don't have to look far in popular culture to see the glorification of what Stan Goff calls the "macho death-cult."
So the doctor has a point. Nevertheless it's a bit unerving having a psychologist criticizing comics given the history of psychiatrist Fredric Wertham's successful crusade to get comics censored back in the fifties. Nothing like that is likely to happen again, and the doctor isn't calling for censorship, just a return to Silver Age sensibilities. But I still think it's best to let the publishers print what they want. If you don't like it just don't read it.
Update: The Beeb covered this story, too, and has a short audio clip to go with it.