I don't know his heart or his intentions. If I had to guess, I think he's "offended" by the commercialism of Santa and the taking away of Jesus Christ. I can sympathize to some degree with his offense... I don't condone what he does but I can't necessarily condemn him either, other than he should have direct his message to the parents and not the children.
I agree that there are much better ways he could deliver the message in a more receptive way. However, I don't think it's "cruel" what he did... If anything I think it's humorous. Really... think about it... He's in the mall trying to convince people there is no such thing as Santa Claus... I know people love to exercise their right to be offended (the man is offended by Santa and the people are offended he is exercising his rights to free speech) but come on...
How many safe places do we need? Every time a group of people say something we disagree with we cry out for a safe place... To say "He doesn't have the right to tell other people's kids what is true..."... well, the founding father's disagree with you. Now, they don't have to DO what he says, but this man has every right to say anything (as long as it's not threatening) that he beliefs and feels. The people have a few choices to make... Leave the mall, request the mall security ask him to stop, or try to deny him his right to free speech by physical force or by communication.