Well, I'm pretty sure when people registered for their exchange, they agreed to the terms and conditions of that exchange. And those terms allow exchanges to decide what transactions are allowed or not. I agree that Coinbase has been much nicer and more communicative, however Coinbase lost a lot of money when ethereum hard forked, which is probably why they care so much now, I'm not sure it's about being honest/communicative...
About Bittrex being unethical: if their terms and conditions stipulate they can do what they did, there's nothing wrong with this.
BTW:

1. This is real life, real money; be aware of what you're agreeing to when you sign up on an exchange. Their exchange, their rules
2. Keeping crypto-currencies on an exchange is a horrible idea in the first place. Exchanges can be hacked, or worse, the owner of the private keys can simply steal your money (Mt.Gox). If you lose the coins, it's your fault and your fault alone.