I still think that if it is legal, more people would use it.
correct answer often comes from the minority of voters.
I voted 'correct'
The correct sentence would be:
"I still think that if it were legal, more people would use it".
Touche' MrTrilby. Of course, I personally prefer the "were" in reference to the "if".
I'd use was with "it."
I second MrTrilbi