This argument would be more valid if it was a phone call. Phone call need or desire am immediate response or as soon as possible.
If you don't require a response or you don't need to an immediate response texting is the most appropriate method. If the message needs to be received and or responded within 6 hr time frame, use a text message. 24 hours or more use an e-mail. You respond to a text at the at the first convenient moment. Driving is not is not that kind of moments.
If you need to get a message to someone and you know he's driving a text message is the most appropriate and responsible method to use. If you receive a text while driving, responding to it when you stop for food, gas, a rest stop, or when arrive at your destination is a perfectly socially except able response. If you stupid enough to put your self and others at risk by immediately responding to a message that doesn't demand an immediate response, you are solely responsible. If some one is texting you with the expectation of an immediate response. You need to tell them they're wrong.