The tiefling situation is painfully simple. I am kind of surprised so many people are getting hung up on this.
Yes, they are the product of infernal powers. Yes, they carry the mark of the Hells upon them because of this. But no, they are not subjects of evil. Tieflings are basically just normal people who carry a curse that makes them look fiendish and gives them some minor infernal powers.
If anyone remembers that Van Helsing movie this quote is pretty apt.
"Evil may have created it. Evil may have left its mark on it. But evil does not rule it, and so I cannot destroy it."
