This makes no sense. Its recommended to have all tires matching, but not mandatory.
The car will drive fine under normal driving conditions. Of course the possibility of getting a flat on the two non-rft, but it really wont make a huge difference. RFT are heavier then non-rft. If that is your situation then go for it. if you have the money then of course match them. You're not going to die or mess up any mechanical like these people make it seem.