2. You don't know where he's been.
3. Mommy could do better.
4. Mommy is married.
5. Santa is a married man.
6. Santa is magic.
Kissing someone or some...thing that's magic seems like it could have any number of terrifying consequences. Maybe you yourself become immortal. Maybe you yourself have to take on the duties of Santa, Tim Allen style. Who's to say? Magic kissing is uncharted territory. Science can't help you now.