In a nut-shell, if you believe stealing is okay under certain circumstance due to some subjective morality you hold, you cannot condemn others holding the same belief based on their own subjective mortality.
For example you believe stealing is okay because the target is a corporation. Maybe someone else believes stealing is okay if it’s from someone outside their cultural group. You say, “hey it’s not right to steal from someone just because of some subjective value that you hold!” But it’s a contradiction because you believe stealing is okay based on your own subjective morality regarding corporations (which are recognized as people under law). Same goes for people that steal from the government, their parents, etc.
This isn’t a slippery slope argument, this is a question of ethics. What I’m saying is stealing is unethical, and not by contrast immoral.