You are assuming that the luck from a luck potion tracks the drinker's extrapolated volition, rather than just the luck potion's inventor's idea of a Nice Thing to Happen.

After all, you would rather not win the Quiddich match, if doing so would lead to your defeated opponent dropping out of art school to go hang out in beer halls.

I guess MOR's Harry hasn't realized this yet, but readers of Less Wrong should.