They were all adults. I don't see the problem.
On the show, it defs needed this ending to be set. As many have said it has gone on a few seasons too long. I am glad that they get another season to wrap it up rather than ending it this season though, but like someone mentioned they better reveal the mother this season and show their path to marriage a bit ect
Barney gets girls into bed by lying to them and tricking them.
Saying girls are something to get '7 from 7' from is treating them like objects. And it's not something to tell our kids about.
It was a moment when the others stopped being disgusted at how terrible a person Barney is and encouraged it instead.