Really, why not have it? Seriously, if I want my troops to go somewhere, I expect them to do the utmost of their ability to complete my movement order. If I wanted them to retreat, I expect them to be smart and not to run a mile around a fence in order to SURVIVE. It's the same as arguing for less freedom of movement. In the end, what harm could this cause if this was to make it into the game? If you want to limit some freedom of movement, let it be up to the mapmaker's craft. There's literally no harm to this other than freeing up APM to be used elsewhere.
You know what would happen? Units will vault unnecessarily as they will try to go back to base or retreat point on the most linear way. You would also get wipes as you need to have the whole squad finish up the animation of jumping the fence which is pretty easy to hit with AoE.
People should either: clear the path with vehicles/indirect fire or be careful with over-extensions. You can always vault and retreat.
Retreat is not meant to be a save my squad button.
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