They understand the ramifications. The same considerations that apply to the President of the United States obviously apply to other dignitaries and potentates. Carried to the next level, I imagine that just about every airline flight carries someone who has enemies. Drug lords, prosecuting attorneys, whatever. If FAA gives the bad guys this tool, they will use it.
Several scenarios come to mind.
All it would take is a terrorist who knows how to fly a light aircraft. Buy one, or rent one, or steal one, there are 200,000 of them in this country. Then just fly it thru the windshield of the airliner. We tend to think of airliners at high cruising altitudes, beyond the reach of recip aircraft, yet the fact is that the point where the airliner is most vulnerable is on final approach. On the localizer, on glide slope, near minimum speed, and with gear, flaps, slats, and everything else hanging out.