Thanks to everyone for their responses. I see and understand both sides of the issue. However, I won't let this stop me from taking pictures from public property.
There were "no trespassing" signs posted at this site, which I obeyed. I know how railroads are about people on their property, and I respect that.. it's for my safety. I do just fine with the great zoom on my camera.
If they had asked a few questions, they would have found that I was an Aerospace Engineering student at the state university 10 minutes from their facility. I wouldn't go through all that trouble to create an alaby for taking pictures of a railroad facility in MS. I offered to show them my pictures, but they weren't interested. Paranoia is the right term for it. I agree that if they didn't want their operations to be seen, they should build a wall or solid fence around their facility. When I drive by railroad operatioons, am I supposed to sheild my eyes from what I might see? What if instead of a camera, I had pulled a weapon out of my car? What could they do to stop me anyways? I sat there and took pics for 10 minutes before I was apprehended. Vigilence is great, but what does it boil down to, besides a false sense of security? They couldn't prevent a harmless college student from leaving with images. How would they accomplish site security when it comes to real terroists?
This has been a great lesson to me. I consider myself to fall on the conservative side. I didn't pay much attention to to the people complaining about the HSA, and I figured that if one was doing nothing wrong, he or she had nothing to worry about it. Call me overly trusting. I still see the need for the HSA, and I agree that the railroad employees did the right thing by coming out to see what I was up to. I like to see that they are on the lookout. However, they crossed the line when they disallowed my photography. Like I said, the evil aspects fof the HSA never bothered me until I was confronted by them. It's really quite humbling, really. It made me really examine my own political views.
I'd like to become more versed on the legality of what they did with regards to the HSA for any future encounters. I want to stand for my rights, but first I need to become more educated, and I realize this.