Smartcookie, I would hate to be the friend who makes people feel they must walk around on eggshells around me. People eventually begin to resent that person for not allowing them to feel and enjoy their simcha publicly and to the fullest. So while I see your point, I too, respectfully and strongly disagree with you. Better that those friends should stay home and not cause the baal simcha to feel bad for expressing his own joy.
I have three children as yet unmarried, two are girls in the older category. Hashem knows my true heart, that every single wedding I go to, and even where the kallah is very young (meaning 19-22), I am VERY much b’simcha for my friends who are zochim to marry off that child. I daven that I would likewise be zochah, but I would hate to see myself as a person who cannot feel joy for others,even when I am not feeling it (yet) for myself. And even more, I would HATE for my friends to feel they could not share good news of theirs with me, for fear that it will “hurt” me to hear it. I believe that every mazel tov we wish others with a full heart, is credited to us, that we should hear it from others, as well.