Was my question too simple for you?
Answer it.
Realizing, of course, that the WTC skin had lots of windows.
And again, the airliners were moving at something like 500 mph.
#1 specious argument, "OH BUT THE PLANE WAS GOING SOOOO FAST!"
This is a matter of the strength of materials, speed alone does not impart any special qualities to anything. PERIOD!
http://911research.wtc7.net/mirrors/guardian2/wtc/fig-2-3.jpg
Note the steel box column construction, the force required to break these columns would exceed the strength of the aluminum aircraft by orders of magnitude.
also, have you ever been up in a skyscraper? and noticed the windows, these windows would NOT be easy to break, they are quite thick and heavy because they have to withstand bird strikes and high winds and the ordinary plate glass like you see in your home windows would not do the job.
You have not even touched upon the HOLLOW POINT issue because its a big obvious glaring fault in this whole business, the airliners nose would have mushroomed out in response to striking the wall and would have spread out the surface area of the airliners attempt to penetrate the wall, in addition to breaking the monocoque structure of the aircraft and also as the aircraft struck the wall, it would decelerate and at such a rate as to cause total global structural failure of the airframe. in short, it would smash itself to bits against the wall causing minimal damage to the skyscraper and depositing most of the aircraft wreckage outside the building.