Q: Why you revealed a trick without the creator’s permission? That is immoral.
A: Since when the competition have to ask permission from the creator to come up with their own copy of somebody else’s idea? How many products had copied Coca-Cola, Ketchup, Corn Flakes or medicines (among many others)? Is consumers’ decision to decide which product they consumed, not the marketed one.
Let’s be honest here, many magicians (or maybe all of them) revealed tricks in private, in class or in lectures without the creator’s permission. And just because I am doing it in public for free, doesn’t make it any better or worse morally or legally. If for you this still a moral issue just because I am doing it public, remember your premise is about asking for permission, not the circumstances they get exposed.
If for you is a moral issue, then why magicians who explain tricks in private, or in a closed lecture is not wrong (which as far as I am concern 97% of the times is done without the creator's permission)? Is it just because they don't do it for free nor in public? Then your concern is not a moral issue but selfish one.
If it really is a moral issue, and you support general competition, then that is hypocrisy. And if you still don't support general competition (regardless their taste, price or quality), then, are all those people who support it (for quality or economic issues) immoral?
Some people are too shallow and act on the basis of feeling without enough scrutiny. For some, this may be better (because is free) or worse for others (because is free & public). In my personal experience, when people complain is because either they already paid for it or because they already know how is done and don't want anybody else to know, and the original premise of this question becomes a secondary issue because is a matter of selfishness and not a matter of morality.