I dunno seems like you're working off the assumption that they lied about the event then threw a chaotic wedding that put the venue under more stress and liability than a regular event. But you have no more proof of that than I do for my assumption.

So how about a compromise, venues should put a clause in their contract that extra fees will apply for a number of different circumstances that apply to any kind of event. Fight breaks out? The price just went up. Unruly demands? The price just went up. But if people just want to have a chill wedding at a venue and cause no trouble there is absolutely no reason they should be charged twice the normal rate. Any event with a large number of people drinking and dancing carries the same risk yet those aren't upcharged only weddings are upcharged because, much like the funeral industry, people are stressed out and desperate to get things booked and organized. There are a lot of hypthoeticals being thrown around but I haven't seen any concrete evidence that a wedding is inherently more stressful for the staff. 100 people at a wedding requires the same staff as 100 people at a birthday, event companies don't suddenly lower their standards/service because it's not a wedding, people at a birthday party still expect professionalism and outstanding service.