If Victoria had just been petty and jealous because Ted and Robin used to date, I would have a different take on this.

But not only were Ted and Victoria extremely good together (I consider her his best relationship second only to Tracey) but she was kind to Robin even after everything that happened and she never threw a fit or guilt tripped anyone.

But this wasn't about being jealous of an ex-girlfriend. Robin was literally the person Ted cheated with when he broke Victoria's heart.

I don't have any problem with my spouse hanging around his exes. It doesn't make me feel insecure at all. But if he cheated on me with someone and then insisted on keeping them in our friend group I would be really really upset. I would constantly be wondering if one day he would choose her over me… again.

Even near the end, when Ted finally tells Robin about it, Robin says "I wouldn't have liked it, but I would've understood!" Even Robin understands why Victoria needed this and would have supported Ted if he chose to go that direction.