Okay, so something that I notice about Bluestar's Prophecy is a lot of people saying that they don't see how Thistleclaw is evil. It's not always obvious, but there were hints. Look at how much he influenced Tigerclaw and what HE later went on to do. Look at how he died. Look at what happened in Crookedstar's Promise when he was seen training in the Dark Forest with Mapleshade. Now, none of these are concrete and here's hoping I have a good example for why.
I think that (yes, the Erins did a terrible job with showing this) Thistleclaw had the potential to go a lot further than he did. His bloodlust was on clear display in the small examples given through the super editions (and for the love of God, HE MENTORED TIGERCLAW. Tigerclaw didn't have a father figure. Who do you think manipulated him into who he became?) But I believe that the reason he didn't go further than what was merely hinted at was because of Goosefeather. Ah, Goosefeather. Here you have a cat who is basically able to see the future through the prophecies that he is given. So from the second Thistleclaw was born, Goosefeather knew his fate. And got Bluestar to block him at Every. Single. Turn. Any possibility of Thistleclaw acting on a whim would lead down a darker path (keeping Goosefeather's powers in mind) and since no one would listen to the crazy old medicine cat, he made damn sure that Thistleclaw never had a chance.
When Bluestar wanted her own life and her own family?
Nope! "Fire must burn without bonds."
That wasn't a choice that she made easily. It was Goosefeather saying "get rid of those things and complete my prophecy or I'll do it for you."
Thistleclaw... Fate just had it out for Thistleclaw (especially in terms of Snowfur.)