1. BitCoin isn't money, not for US company. Neither other tokens.
So? That doesn't matter... Not only money can be stolen. Stealing a bitcoin, stealing a car, stealing your shoes is still a stealing...
2. Even if BitCoins were considered as money, they would still require full compliance with KYC/AML.
That doesn't give someone a right to steal, block someone's money. They shouldn't accept money from unverified accounts at all if they have such policy. They have no legal right to block someone's money at all. They can block account, but should return the money.
I agree - stealing is bad.
But true nature of a problem as usual lies in it's definition.
You treat BTC as you would treat money (because in essence that what BTC is). However from the legal standpoint BTC isn't money and can be legally treated vastly different (banks and other entities are bound by law to exchange money for goods and services, and can be prosecuted to do stuff with your money).
In other words you can't do with money things you can do with coins and vice-versa. For example - they (Bittrex) can accept BTC, and then suddenly suspend your account without giving you reason for suspension (they wouldn't be able to do that with money). In this case they are not locking your money, they locking your "THING" and they can, for example, tell you that they have lost your "THING" in a fire and pay you back for it with the amount that thing was worth when you deposited it (That's one terrible scenario I expect to see in this situation). Or they can hold that "THING" because it may fit into some digital goods export limitation to certain countries like Iran. You can't and never should call BitCoin money if you have anything to do with jurisdiction that does not agree with you on that account.
Remember, when you giving some service your BTCs you automatically agree to play the game by their rules, and usually rules are rigged in their favor. I don't really see any viable solution to enforce BTC back from bittrex at this point, I'm 99% positive any lawsuit will fail because of their TOS and legal status of BTC in US.
That's bitter and suck and bad and all. But that's what other countries get when they deal with US nowadays.