Notwithstanding the histrionics by some about the scanning (which, I state again, is voluntary), I think the conventional wisdom that airport security is a huge hassle for air travel is not shared by those who regularly travel by air.
I don't fly very often - maybe once or twice a year. But from my experience, the real problem with airports security stems from inexperienced or just plain stupid, selfish flyers. They generally think the following:
1) I'm not going to bother to find out about any security regulations ahead of time- after all, I don't care what the "policies" are for the companies I deal with every day- I just argue until I get my way, so I'm sure that will work with TSA agents too. I'm not going to bother to read any of the signs posted EVERYWHERE about which liquids can go on the plane, and in which amounts. So, I'm going to needle and whine with the TSA agent who tells me that I can't take my 128 oz. "Abyss Boy" drink on the airplane, even though his slows the line down for everybody.
2) I need my ID and my boarding pass? Well, shoot, those are in my carry-on. Just give me a second. It's in here somewhere. Shoot, did I leave my wallet at home?
3) I paid for this seat. If I want to recline it in your face for the entire flight, well that's my right!
4) I don't want to check luggage, so I bought the biggest suitcase I could find, and I'm going to carry it on! If it doesn't fit in the overhead bins... well, I'll just leave it hanging out into the aisle, over a different row, and let the flight attendant take care of it (and by the way, the carry-on is over your seat because I need the space over MY seat for my "personal item").
Taking a train allows me to avoid all that sort of nonsense. I get all the seat room and luggage room I need, and I rarely get held back due to another passenger's stupidity.