If my parents were normal, I would think about it, but they frankly are not. I told them, the last time I saw them face-to-face, exactly this: "You are letting my younger brother, with his drinking and his drug habit, take over your entire life. You are going to keep on forgiving him every single time he tells you 'I've come to Jesus, I love Jesus, and Jesus has healed me'; no matter how many times this turns out to be a lie, you will continue believing it. His behavior will get worse, and ultimately, he will run you out of your own home. Because I know precisely how misguided you people are and how screwed-up your priorities are, I know that even losing your home to this twit will not stop you from continuing to give him money. You are conservative Protestants, and you can't help it. You are mentally fucked-up, and I do not have the power to help you." And I turned on my heel and left. At the time, I had blood streaming from my nose from the latest episode of domestic violence. That prophecy came true in every single detail, by the way, because I had known those people my entire life. I just knew. No, I'm not going to tell them I'm a zoo.
I think that whether or not you end up telling your parents comes down to multiple factors, but those must include your own level of financial independence, how successful your parents have been at winning over your trust, and whether or not your parents have likewise been open with you about their own various levels of deviance. If I had parents who were able to talk with me openly about the fact that they once experimented with BDSM or something or were a part of the Free Love Movement, who were absolutely liberal, whom I knew had offbeat views, I would probably tell them in a skinny minute.
I don't think that this should be completely on us zoophiles to decide. Our parents have to do their part to win over our trust, and if they have not, then we cannot be blamed for not trusting them.
Then again, if your parents have worked hard to reach out to you with trust and reciprocity, then if you feel ready to try to meet them halfway, then they deserve your trust. If they've given you a chance, then they deserve a chance.
Still, that level of financial independence is a big deal. If we can't stand toe-to-toe with them as equals, then that really makes it hard to be assertive about our beliefs without sounding even to ourselves like ungrateful brats. That's just reality.
However, just to be clear, there's meeting someone halfway, and there is flying all the way across the Atlantic Ocean by flapping one's arms. There is a difference. Too wide of a gulf from a lack of trust is just not going to be bridged. We cannot be blamed for not wanting to trust this part of ourselves with someone we wouldn't trust with far less.