Should senior "proms" be banned for Jews?
In a word, no. There is no obligation for Jews at these proms to dance or dress immodestly, what is the problem with Jews attending social events and having a good time?
You are not Jewish. Who gave you the authority to decide Jewish Law?
There is nothing wrong with attending social events. The problem is that men and women dancing together is immodest, period. Men aren't even supposed to see women dancing among women because it is immodest to see the form of a woman dancing. That is why the mechitza at a Jewish wedding is not made so you can see through it but the mechitza in a synagogue is made with wholes where the women can look across and see the men praying. The second is fine as long as the men don't stare at the women through the wholes. It's just meant to keep a separation between the genders.
This is my Gentile point of view, your question by using the word "Should" is implying that you are inviting all points of view, and this is mine. I simply can't believe that dancing is immodest! Is going to watch the ballet forbidden? Social events are, by definition, social, and I would say that it is morally wrong for Jews to be forbidden from mixing with Gentiles on account of this. However, this is coming from my position as a Gentile (as I cannot see why this is immodest) and I respect your views, even though I would disagree with them.