If I may clear up some questions...
These protesters are against, like, everything. They protest other conventions, Christian groups, even Christmas in the Park. All they care about is that there are a lot of people outside - they don't care that you're into anime, cosplay, or whatever.
These protesters are essentially trolls. They document everything and are just waiting to catch their martyrdom on camera. Pretending they don't exist is the best way to respond.
These protesters are very well-trained and well-prepared. They have heard everything you can think of and already have responses waiting. They have been doing this for years, and there is nothing new or clever you can say to make them leave or change their mind.
Arguing, counter-protesting, or simply talking to them is futile. They won't be persuaded. And whenever you engage with them, you're letting them win.
They are 100% legal and they work hard to remain legal. They're very careful, so we can't simply tell them to leave, or call the cops. But that said...
We are working on several fixes for this situation, and we have a lot of really great ideas to try next year. I'll be sad that there won't be the hilarious mashups with the Jesus cosplayers, but it's worth it to ensure our attendees have a great time and don't get bothered by jerks.