Lets get to the bones of this.
Compare a light aircraft with a white van.
The white van can be nicked from any where. None are secure, every van is vunerable. Having nicked the van there is all the time in the world to make preparations in terms of installing a bomb or other device.
An aircraft can equally be nicked, but there are some problems. There is already a greater chance someone will ask what you are doing or become suspicious. I can think of a lot of smaller airports with the A/G operator knows the voice of every owner pilot for example. Having nicked said plane if there are any preparations to be made the aircraft has to land somewhere before the "attack". The said "nicking" also requires rather more specialist knowledge than said white van.
So why would a terorists choice a light aircraft over a white van.
They both have the potential to cause chaos.
The aircraft is unlikely to cause any more chaos than the van. In fact the evidence would suggest as a delivery vehicle it is far less precise and the outcome far less predictable.
There is an exception, an obvious one concerned with aerial contamination where the light aircraft could have an "advanatge", although that advantage is not necessarily significant and is likely to be more trouble than the advantage is potentially worth.
Airports with more limited security almost without exception can handle nothing larger than a light twin. The risk associated with a larger jet is different and undoubtedly a larger jet has the ability to carry a payload significantly greater than a light twin or single. However, the security measures in place at larger airports are significanlty different to those at farm strips.
Politicians have a responsibility to deal with the evidence - if they dont they are likely to end up like Tone, fighting a war based on evidence that did not exist - hardly an accolade of which to be proud, even if it might not have been "his fault", for that he will always be remembered.