Decorator crab- should he stay or should he go

After feeding my tank this afternoon I noticed a new hitchiker. A decorator crab about the size of a nickel. He's quite fascinating to watch. Thankfully none of mycoral was stuck to him. Well I snatched him out but I'm feeling kind of bad. I don't have a sump for him yet so it's either back in the tank or the royal flush. I've got a gorilla crab I'm trying to catch also. And either a pistol shrimp or a mantis. Is a pistol shrimp really reef safe? The **** emerald crab I bought to eat bubble alage at my acan coral and he was sposed to be reef safe.so Should I put the decorator crab back in or flush him ( and why do I feel bad about it when I eat crab legs all the time anyhow ?) ugg