There's a good side and a bad side to government contracting, like anything else in the real world. The biggest valid reason the government uses it is so they don't take on people for a whole civil service career just to do a project that's going to take six months or two years or ten years, or even indefinite but it'll still be cheaper and more flexible to do with contract labor.
After all, you can change the mix of skills and positions overnight with a contractor, instead of a year of lead time and retraining with civil service, and the government doesn't end up with the back-end legacy costs of retirement, benefits, etc. or the front-end HR costs of managing the workers.
Which all means HELL NO they aren't secure jobs. And, in defense of the contractors, the Federal government can be an arbitrary and unnecessarily demanding master in ways that no private sector organization could get away with in a million years.