How Halloween is celebrated today goes back to the time when ancient pagans believed that October 31 is the day when the boundary between the living and the dead dissolves. Since the dead could cause harm to those who are living, people will go out into the streets wearing costumes and masks to ward off the evil spirits.
Why it started and why it is celebrated today are two very different reasons. In a nut shell it started with superstition. Today it about nostalgia, having fun, and being creative. As for the candy, though offerings may have been offered at one time, it is not the reason we do it today. "trick or treat." think about what you are saying. In the beginning there were no treats handed out during this holiday. As Halloween evolved there was a time period were mischief went too far, property was damaged and people got hurt. At this point a woman bribed the local kids with treats, and it worked. Nothing of her was damaged. She published this in a journal and more and more people caught on. They would give the kids treats as a bribe. So, trick (I will play a prank on you) or treat (bribe me with some treats and I will leave you alone). This holiday is kind of fascinating to learn about. How we get our traditions today, how it went back and forth from a child's holiday to an adults holiday. If you are interested you should do some research in it, I found it neat; but then again I study history. Oh as for if it is a blasphemous holiday, I don't fill that conviction. God bless