No, because there are ramifications outside of just losing 8 hours of billable time. You don't have colleagues who can take over your responsibilities or who can maintain without your involvement at a moment's notice like you have in a robust corporate environment. It takes a lot of work, notice, and involvement to schedule a day off, you worry about the way it will affect the perception of the clientele, and you lose the 8 hours of billable time. There is much more stress and much different potential long-term consequences of taking a day off as a self-employed individual than as an externally-employed individual.

It seems to be a psychological thing. If you get a higher hourly/daily rate to make up for the lack of traditional PTO, you feel even worse about taking unpaid time off because you're "losing" even more money.