Trains have degraded security though. Once a plane leaves, someone has to be on the plane or have had access to it beforehand to affect the flight. You can defend against this through security at those specific points. On a train, the entire trip is over miles of tracks which 'anyone' can access. Security at boarding doesn't affect the attack surface area as much.
> On a train, the entire trip is over miles of tracks which 'anyone' can access
Indeed, but trains, even high speed ones, are also very robust compared to airplanes.
Even if somebody does manage to get access to the track (not so trivial in many cases), and trigger an explosion on the track with good enough timing to catch the train as it goes by, and manage to derail it, there's still a good chance that all or most passengers would survive the crash.
Similarly, with the size of bomb one might smuggle on board a train, the likely effect would be to just kill a few passengers in the immediate vicinity of the explosion; the train itself would probably be just fine. So basically not much different than setting off an explosion at a random restaurant...
For a terrorist, the odds just aren't all that great with trains, which presumably is why there have been so few attempts at doing such a thing. One of the reasons terrorism is so scary on airplanes is that they feel (and are) so fragile that it magnifies the effect of any attack greatly.
"Degrading" security not "degraded" security. I think the post you are replying to is implying that they would rather take the small risk of being blown up on a train over the certainty of being treated like a terrorist at the airport.
That said, I might prefer train travel to flying.