And your alternative is...what, again?
Life is risky. This is *exactly* the sort of strategy that should be adopted. Current texting laws are essentially slaps on the wrist, and there's too much leeway to get around them (for good reason, as I should not have to disclose the contents of my cell phone when I've done nothing wrong that you can prove). If, however, the individual DOES do something wrong (hitting a pedestrian, if found to be at fault in an accident, runs off the road, etc.), then I have no problem with allowing evidence to be introduced as to their behavior.
The law already makes a distinction about your thoughts and motives when committing a crime, even when the actions themselves are not crimes. Acting in a thoroughly reckless manner that results in someone's death (driving down the interstate at 150mph and hitting another vehicle, for example) can up the charge from manslaugter to murder simply because you were acting with such a willful disregard for the safety of others (in fact, in most states it's referred to as something along the lines of "depraved indifference murder"). While I don't know that I feel that texting while driving should (or shouldn't) rise to that level, I don't take issue with adjusting the charge or punishment based upon the fact that you were engaging in an activity that is known to raise the danger level substantially.