I don't know, we (and yes, the government is us) clearly have an interest in encouraging families raising children, buying homes, etc. It's good for the economy.
Offering tax incentives are a good way to do that. No one decides to have kids because they get a tax break but if you're in the position where you're trying to decide if you should have kids now or wait a couple years, a relatively small tax break might be enough to allow you to do it now. Same with a home purchase.
The idea that we would live in a world with no income tax deductions is kind of unrealistic.