[shantly]

The generous view of the dads worried about sons playing with girls' toys (no quotes around girls', because I guarantee the marketers intended them that way) is that they're concerned it'll signal "ostracize me and kick my ass, please; I'm an easy mark for gaining social status at the expense of another" to their peer group. Which doesn't make the effect any different, but the intent might not be to limit their sons' play per se.

[edit] what I mean is simply that those kinds of sentiments might be a reaction to perceived bias in culture, expressed as bias but not driven by same, if that makes sense. A kind of re-enforcing meta-bias. Again, doesn't make the effect any better.