I guess when it comes to attractive men or rather men more likely to be viewed as attractive by women, it unsettles other cishet men because they’re the ones who’re supposed to be doing the gazing and perhaps because of jealousy. That Justin Bieber seems to have way more female admirers than say said neckbeard will ever do.
Certain male heartthrobs would fight to be taken real seriously by the music press. David Sylvian’s a musician who was considered the most beautiful man in music fought his way to be respected. He eventually earned it and overturned his reputation. Similar things can be said of Justin Timberlake.
Then there’s the type of man that’s really appealing to straight men but bewildering to women. He’s a power fantasy that cishet men that live vicariously through. A kind of quasi-brother or father figure for them. Their role model. It’s not bad but it says a lot about whether if men are objectified or not.
If he gets sexualised by most women, men would find him revolting. Their role model has been defiled, emasculated and beaten. That blows their self esteem and also their ideals as well.