Earlier quoted context omitted.
I get what you're saying, but contractors by their nature tend to be mobile and motivated by pay. This strongly increases the likelihood of an outflow, especially if companies don't react to the extra taxes by raising pay. The effect is compounded because a) good techies really like to work with other good techies and b) losing most of the good ones also means losing all of the people who can recognize other good tec…
Contractors are mobile in the sense that they can change company every 3 months. They stay in the same area. They are not mobile to move themselves and their family across the border periodically.
I don't doubt that there will always be some that won't or can't cross a border though.