Because I own the machine that runs the code. It's that simple. Their code will do what I allow it to do. It's not really a "take it or leave it" deal. I have numerous options available to me. If those options aren't there, it means I don't own the machine.

If they don't want others to "tamper" with their code, they should run it on their computers. Keep them safe and secure on their servers. Code that runs on our machines is and should be completely under our control. Anything that enables them to usurp this control from us is an attack on computing freedom and should be illegal.