Well, I don't like underpants either, but I wore them on the Camino.
For one thing, you are going to SWEAT while walking, which will lead to CHAFING with skin on skin. Something absorbent might be more comfortable.
The other issue is that it could make undressing for bed an issue. Often, people change clothes right beside their bed in the albergue and while you may not be embarrassed at your bare tail, it could cause discomfort among fellow pilgrims who aren't as progressive :lol:
Lastly, if you DO decide to go bare, you can always buy panties along the way. But they're so lightweight, it seems silly to go without them, to me.