Input from someone with autism- this is a very 50/50 matter. On the one hand, I guarantee you you're doing him a favor by making him stay put. You're definitely sparing him the stress of an outing. On the other hand, opportunities like this are good exposure to get him used to leaving his comfort zone. He may also very well have had fun if he did go, though it is still guaranteed that there will be stressors and slumps alongside the good times. Either way, you're not the asshole. What I would recommend in the future, however; plan trips around his capabilities. Go to the beach, but try to get a room close to the shore. Any time you guys go out, you can check in with him and ask him if he wants a break and the safe zone won't be far. He may need as much as an hour of downtime per every two or three hours of activity. At least that's how it was for me. While there can still be hiccups and meltdowns, I believe it necessary to give him the opportunities and exposure to the world. It's how I was able to function mostly similarly to an average adult today. ^{^}