I agree that you need to charge what you feel comfortable with, but for those who suggest that $50 / hour is too much, please consider the following...
First, for some people who tutor (like myself) it is a primary income. And, if you claim the income on your taxes (like I do) then you are earning even less than what you charge. And if you spend time outside of the tutoring session to communicate with teachers, prepare materials, etc. (like I do, your "hourly" rate diminishes as well. So my $50 / hour really equates to somewhere between $10 and $15 per hour "net" when I take out taxes and divide my rate over the time I actually spend preparing for my students. It's hard to live on $10-$15 hour! So just because some of us charge more than $10 - $20 per hour for tutoring doesn't mean we love our subject or our students any less than anyone else does, it simply means that we need to be able to make enough money to survive.
I realize I could charge much, much more than I do. There is another tutor in our area that charges as much as $90 hour for math tutoring. The only way to get his rate down is to commit to a full year or full semester of tutoring and you have to pay the entire amount up front! And even with that his lowest rate is $70 / hour. And his schedule stays full. I feel good with what I am charging. It's been the same amount for 6 years now and I have students who have stayed with me from middle school all the way through high school, so apparently my rate is not out of line.
Think about how much we spend on our children to play sports, take music lessons, etc. It is a small fortune. Isn't their academic performance just as important?
So bottom line, yes, charge what you feel comfortable charging. You need to sound confident when you talk to parents and they ask for your rate. But before you "low ball" yourself think about what you will actually earn when all your time and taxes are taken into account. You need to be able to "afford" to work after all!