There are many reasons why the idea of telling young children that some fantasy creature is real is a bad idea.
The first is that kids minds are developing and taking in information when they are young. When kids are learning about life, and how the world works, they shouldn't be taught that it is possible for someone to fly to every house in just one night.
The second reason is that it can cause conflict with kids. There are some kids who know Santa isn't real at a young age, and are teased or mocked because of it. When kids get older, some still believe that Santa is real, and likewise, are teased and mocked for it. I have seen both.
The third reason is that it's just for business. Many companies sell their products by exploiting kids gullibility, like mall Santas, and many Christmas products. A recent Macy's commercial consisted of kids talking about Santa, and how they believe in him, and their project to "keep the dream alive" which is obviously using kids innocence to sell products.
The fourth reason is why would you tell a lie if it could only bring false hope and break little kids hearts a few years later? It is simple. It is lying to kids for no good reason other than temporary happiness that would all be ruined. Its not even good for the adults either. The parents have to buy presents because their kids believe some myth.
The people who make the toys, people in factories, people who work many hours, every day, little pay, get no credit, because apparently "the elves" made the toys.
In conclusion, the myth of Santa Claus is not beneficial to kids or adults in any way.