Yelling at them isn't "success," it's in essence invalidating what they feel, dismissing them, and giving them the impression they should simply remain silent. If that's you're intent, then yes you would succed by yelling at them. I've had a great deal of success helping men like them, IRL. Can you say the same?

the idea of dick size or breast size mattering is a complete societal fabrication

This post, the other 9 you referred to, not to mention countless posts and conversations on the subject show it's not a "complete societal fabrication."

If your partner(s) is/are happy then who cares?

Clearly, they (the man) does. If his partner prefers bigger than him, and he doesn't want to be settled for in that aspect, he has every right to feel that way. Again, trying to invalidate how they feel does nothing to help them. It just causes them to shutdown.

Yes, some of these men are desperately lonely and may blame this on their small penis, but judging by the behavior displayed and the dismissive tone taken to anyone who tells them that there are many women don't really care over much for PiV sex I think their problem lays much more in their attitude then their equipment.

Or it could be those men hear conflicting information, or endured negative experiences that have them firmly feel and believe that way. How many woman state a preference for average or below average, compared to above average? How many studies indicate most women prefer average, compared to studies showing most women have a preference for bigger? Those men read the same reports. Not to mention the descriptions given, between various sizes. Or women saying once they've gone big, they can't go back. I tell those men to literally ignore what women say, when it comes to this subject, as that's exactly what they need to do.

You're combating it, or more to the point them, in a way that isn't helping them. It's more like pouring vinger on papercuts. You're correct coddling won't work, but nor will yelling. Owning a penis doesn't mean you know how to help those men, without actually talking to them, listening to them, and narrowing down why they're insecure, at times to the point of crippling. Best way to help those has nothing to do with reminding them different women prefer different things. It's first getting them to address the depression, remind them what confidence actually means, that they are entitled to feel as they do, and then reminding them what all their options are. It's about telling them how to regain control they never actually lost.

As for the threats made to you, no, there's no excuse of them. I've had a few as well, from men and women.