Pitch invasion before end of game - completely unacceptable, all those idiots deserve to be banned.
Pitch invasion after the end of the game - feels a bit cringeworthy, it's a quarter final after all, but I can understand it given the years of dross we've had to endure. Wouldn't be my first reaction, but I'm 37. Ten years ago, after a day on the sauce, I can see how people could get caught up.
The security element concerns me though in terms of the players/staff. You're not going to get all those people off the pitch, once they're on, but the priority should have been to get both sets of players off the pitch asap as soon as that final whistle went, given it was obvious what was going to happen.