Poloniex is definitely liable they are illegally holding you money without any reason relating to illegal or wrongful doing. They are just basically putting you in a bad position in order to waive your legal rights against them. First off all legal rights are always there it cannot be remove not unless you are involve in a criminal violations. Second any contract agreement related to a removal of rights just to withdraw your own money is basically voidable. So what I am saying is you have another choice. If you accept their terms now you can easily sue them about it after you receive your funds or even if there are any future problems you can't solve because they are bringing up there so-called "agreement" with you.