ZZZ Controller reported pilot refused ATC clearance following an MSAW alert for the aircraft entering a higher MVA resulted in an CFIT event.

Narrative

Aircraft X requested direct an IAF 10 minutes prior which I issued to him not realizing he would clip a 090 ZZZ and he was level at 080. The terrain warning started flashing minutes prior to entering the higher terrain so I issued a 30 degree left turn. The pilot read back the turn then started telling me he had the surrounding terrain in sight. He did not turn so issued it again and issued a climb to 090. He argued and then proceeded to turn right which put him directly into the terrain. I asked him which way he was turning and then tried to give him a harder right turn since he was already in a right turn. He then told me he wanted VFR OTP so I issued it and gave him direct the fix again.I should have double checked his altitude was safe for his route of flight all the way through my airspace. I do believe this was a pilot deviation and I issued the turn multiple times with plenty of time to clear the terrain. He read back the correct turn but decided to argue and then ultimately turned the wrong direction.