The few hundred pound payload of your average light plane pales in comparison.
The damage done is really irrelevant; it's not about killing a maximum number of people of a massive dollar value in property destroyed. It's about terror. That's why it's called terrorism.
Many focus on the damage done to the airlines in the aftermath of 09/11, but the truth is that the effecton general aviation was much greater.
We came very close to not being allowed to fly without a clearance and flight plan, and the public was afraid of light airplanes for a long time. In ag aircraft, we were required to install special disabling devices, and for a time we had to put prop locks on the aircraft.
TFR's like the one in question are common. Look at the DC area. Look at what we had to go through to fly during the olympics. There's nothing unusual in the TFR as presented.
Do something stupid like fly into the TFR area and cause an incident, and no damage needs to be done physically: the resulting fall-out only damages general aviation in the eyes of the public and feeds the media frenzy.
Does a TFR physically stop an aircraft? No. It stops those who honor the TFR. Those who don't get stopped by other means. The TFR excludes those who read and obey. Those who don't become targets of interest. Those that are really interesting may get intercepted, investigated, and even forced down. This isn't a new process. Try flying into a presidential VIP TFR some time and see what that does for you.
You want to see the end of general aviation as we know it? Get six or seven light airplanes around the country and conduct a coordinated attack on a public event or building. Most likely very little damage will be done, but the resulting restrictions that will take place will do severe damage to the industry. See how it affects rentals, charters, ambulance flights, instruction, aerobatics, and a host of other things.
09/11 caused big changes in flight instruction, and shut down a third of the flight schools. It changed a lot of things. I've heard a lot of people opine that light aircraft are no threat; that may be true in some cases, so far as the direct target. It may be very wrong in other cases. But one of the primary victims that would lose in such a case is general aviation, and it would lose in a big way. Forget the actual amount of damage that could be done; the results go much farther than that, and this is the purpose of terrorism. We're still dealing with the after affects of 09/11 today. It could easily be much, much worse, and will get that way if any light aircraft get used for illicit terrorist purposes, even if not a soul gets killed.
Don't underestimate the true consequences. They'll be much worse than you imagine.
The TFR is there for a reason, and it's valid.