As to mortgages and charities, it has been studied that getting rid of mortgage deductions would actually spur homeownership because the people have more disposable income in their pockets, or at least know what their tax expenditures are to better plan a savings plan for down payments. The same could hold true for charities. I have looked at plans that leave only those two in place, and that may be a good compromise, but cut all the other deductions and loopholes.
Charities are a tough one. If I didn't get a deduction for the couple hundred bucks I give to charitable organizations every year, I would still give. Its such a small amount of money that I don't really care too much about the tax savings. But a lot of charities or non-profits are sustained by massive contributions from very wealthy people. For instance, in the hospital in which I work there is a public area that honors anyone who has given more than $1,000,000. These people absolutely would not give that kind of cash if it weren't tax deductible. It would be harmful to a lot of good organizations if the charitable deduction were taken away, but you can't really say that my $100 isn't deductible but her/his $100,000 is. For that reason, I would leave the charity deduction. Europe is a good example. They don't have charitable deductions in any Western European country, and the result is that all the art museums, hospitals, food banks, etc. are run by the governments for the most part. I don't like the look of that for the US, and I'm going to go out on a limb and say you probably don't either.