This was maybe a useful message ten, twenty years ago.
The problem is that, honestly, a lot of these feelings are messy. They aren't expressions of weakness, they aren't some magical key used to unlock progress, they're not even something that's easily sympathized with.
They can be the white-hot anger of being pulled off a project or ignored for the nth time in class or being made fun of. They can be the bubbling cold black rage of being forced to work on something only to have it stunted at every turn by bad management or being shunned by members of the preferred gender for whatever reason. They can be the bright flash of joy and uncontainable exuberance of having pulled off the impossible on deadline or winning a hard contest.
The point is, in all those cases, boys and men who express their feelings honestly and openly are considered creeps, weirdos, crazy, or unprofessional.
So, no, the problem isn't that they keep these feelings bottled up--it's instead that, when they're honest and open in their passion, people become uncomfortable and afraid or inconvenienced. We celebrate the passionate man, in the abstract, but you bet your ass it's never made things better in the day-to-day.
In fact, we tend to double-down on this nonsense, and so punish the behaviors (sparring, yelling, cursing, whatever) that would formerly be used to defuse the feelings in young folks until they realize such things are counterproductive, and bait-n-switch them.