This aspect of us very often offends feelers, but most INTPs aren't trying to shoot you down without compassion or mercy, I promise. INTPs have a love of truth. We view debate (not arguments...not confrontational type stuff, but point/counter-point debate) as an incredible tool to learn. As we mature we have a love of being proven wrong possibly more then we do of convincing that we're right. It's exciting to have our preconceptions truly challenged (and challenging challenges are so rare).
So we play devil's advocate often enough. We appear hostile to types that actively avoid confrontation. Fe types particularly are jostiled by this. Si types tend to view it as an argument when it's really just a debate, and Si can be very argumentative and will get angry at it. SPs generally don't care, and at worst become passive-aggressive as they view it as argumentation too...as hostile when it isn't meant to be.
It's a big reason INTPs can have difficulty with people...we're not being hostile when we're doing it...we're actually pursuing what we see as opportunity for intellectual growth.