I agree with BurmBaroness, it's not absolutely a stressful and hideous idea for all snakes. Yes, some or most wouldn't like being exposed to so many people but there are some snakes that if the owner is careful in how things are done seem to enjoy an outing.
Both my BP's really seem to enjoy going outside for some fresh air when it's warm enough, they are as mellow as when I handle them at home sometimes even more so! They seem to enjoy exploring new grounds and the outdoors. I can't see how an occasional outing can be harmful to a well adjusted snake.
I only do this with my snakes when they seem receptive to it. I only handle them when they come out of their hides on their own and if they seem in a good mood. If not I just leave them be. Most I have to fight to get back into their cages, they don't want to go back!
In a situation where there will be lots of people, I would be especally careful of how close people would get to me. I'm certainly not shy to tell someone to not get too close or act stupid around my snake to freak it out. I also only let very few people touch or handle my snake, I don't like the idea of strangers touching my snake and freaking it out that way either. But I will usually let one or two people that seem alright do so for a couple of minutes. People are very respectful of what I say in my personal experience, if I tell them not to move around too much around the snake with hand gestures, etc. It's amazing to see how well people listen!!! 2 minutes later they're warning everyone else not to do that! lol
Anyways, if your snake seems in a good mood to be handled that day and doesn't seem stressed out I say go ahead and bring him out with you. Try and make it relatively short of an outing and bring along a tote that you can put it back in to relax and hide away if he starts looking uncomfortable also a dish of water that you can offer during the time that you're out. That's what I do anyways. I don't do many public outings if not any these days, I prefer bringing my snakes to my parents house to romp in their yard but if there was some activities just for animals I might consider going.
Keeper of 5 snakes, leopard geckos, 1 green iguana, 20+ tarantulas, 2 dogs & a bunch of rats!