@augustlan When you order a bottle of wine at the fanciest of restaurants there is still wait staff waiting to pour. I think an open bar requires a bartender who serves the crowd, mostly because at weddings people tend to get both lose as well as schnockered when left to their own devices, in order to keep people in check and not be insulting like passing out juice boxes in pre-school, one has to preserve the air of control, amid an atmosphere of freedom.
Meaning bar service! It’s crowd and alcohol control. How can you be certain everyone will get some, how can you be certain there will be enough and how can you be certain that again, left to their own devices that party goers will do the right thing and be responsible and NOT ruin your wedding? Think about it, it happens every day! Not to mention if there are lose bottle of wine laying around that can be dangerous to little kids that are in a family atmosphere and not necessarily watched like hawks.
A glass of alcohol left exposed is one thing, a bottle might be a problem? Just opinion like I said, but there are too many variables, and when it comes to human beings potential to get intoxicated, better to be safe than sorry.