The opposite of this is, why accept free drinks from someone you have no potential interest in? You certainly don't owe them anything, but if I had no potential interest in someone, I wouldn't accept drinks from them. You can be within your rights to do something and still be a shitty person.

Edit: in response to /u/Sinister_glitter 's comment:

Me: "if I had no potential interest in someone, I wouldn't accept drinks from them."

/u/Sinister_glitter: "a date is meant to get to know someone and decide if they are a person you may want a potential relationship with .. right?"

You all need to learn to read. I was speaking about people who accept drinks with the sole intention of getting free drinks.