Magic is a form of entertainment and part of it is its mystery. When the audience say "How did you do that?", that is music to the ears to a magician. Unfortunately some people answer those questions, and sad to say instead of magicians hearing "How did you do that?" they would hear now from one member of the audience "I know how he did it, here let me show you..."
That is an example of an exposure and sad to say a lot of people are actually exposing the tricks because they see it being exposed too. It could be via TV specials or even via the internet. Here are a few people who had been considered as those who actually support exposures.
1. The Masked magician
Also known as Val Valentino, he starred in the FOX TV special Magic's Secrets Finally revealed. That TV special really made a lot of magicians very angry and of course that's the main reason why he hid his identity. He said that he did these exposures to encourage magicians to create new tricks. In my opinion, yes magicians should create new tricks but exposing them is not the proper way to encourage magicians.
2. David J. Castle
David Castle is a magician who has a PhD, unfortunately he exposes tricks via his website. The tricks he exposes are generally easy ones and those that are self working. It might be good for beginner magicians to learn how these tricks work but of course if these beginner magicians started performing those tricks and some of his audience also knows about it, then the purpose of entertaining is defeated. Maybe if his website would at least require a password then that would help more beginners to get into magic.
3. The Trickbusters
Probably the worst breed of exposers of magic tricks. First they are not magicians (a linguist and an engineer) and second they are just plain skeptics. If they don't want to believe then they shouldn't be watching magic in the first place. Their main reason for exposing the tricks is that they make our rational thinking stagnate in a way. I mean they should go read more Science journals that attest to the fact that magic actually helps psychologists understand better the human mind.
I believe the reason why these people still stay in circulation is that some people really appreciate (sadly) what they do. The main reason I believe is that a lot of people think that magic makes a fool out of you but in reality there is a big difference in getting fooled and making yourself a fool.
A magician's job is not to fool people with their tricks rather they mystify at the same time entertain people. If you watch a magic show and let yourself be mystified rather than think that this magician is making a fool out of me, then surely magic would be more entertaining. Entertaining of course is the main reason why magic tricks are done.
So what must we do about these people, who keep on exposing magic tricks? Well, I remember that happened one time when I was performing some tricks for my colleagues in my school organization and of course I was a bit furious but after showing more and more impressive card tricks, that guy just stayed quiet. The answer is continue performing and show to them that no matter how much you expose the tricks you can't bring down one good magician.
Honestly, I don't think exposure will and can be stopped, simply because a lot of people want to know how the trick is done. For some people knowing how the trick is done is the end of it but for some, performing it after knowing how it's done and trying to learn more magic to perform is actually good (in my opinion) because it means that this person has interest in magic.
That's the only good thing I see though about some exposures: making some people go into magic, making it survive for even a longer time.