Another way to look at it, is to compare the situation to renting or leasing a car.
I can lease a Ford Focus for £245/month. This ties me into a 3 year contract. (Similar in some ways to hiring a permanent employee)
On the other hand I can rent one from Sixt, which will cost me £600/month and I can give it back whenever I like. (Similar to hiring a contractor)
It's exactly the same car, the only difference is the terms under which I am getting it, and the flexibility of the contact.
You also need to ask yourself the question, if the ATC service in say Senegal was looking to recruit you on a temporary contract, would you
A.) Want to be paid the same as the local controllers (earning about 1/2 what you do now)
B.) Want to earn the same as you do now (leaving behind a steady job, leaving the family behind, no pension etc.)
C.) Earn more than you do now, to compensate you for living in a foreign land, running 2 houses (one for you, one for the wife and kids back home) lack of pension, and no job security.
It sounds to me like you would, from your principles, want to choose A, but would then decline the job offer because you are better off staying at home.
Which is the crux of the problem.
I work in the supply of temporary staff, our staff are paid 50% to 150% more than permanent staff doing the same job at our clients sites. This is for people with the same training, working in the same building, from the same country, doing the same job.
It is not a foreigner vs. local thing, it is a contractor vs. permanent employee thing.