I disagree with the 'take mom down a peg' line of reasoning. You have to approach it without taking an adversarial stance. You don't need to fight with her about it. You can say that you care about them and you would like her to understand and respect that, but then let it go. If she is afraid or disgusted or just plain thinks its a stupid hobby and a waste of money... well, so what? That's fine. Agree to disagree and don't talk about it anymore. Your relationship with your mom as an adult child is shaped by YOU. Act like a kid-- ie arguing, engaging in power struggles, demanding acceptance, etc-- that's not a grown up relationship. Just state your feelings, state your boundaries and keep them. So if for example, once you've stated your case clearly, she wants to keep arguing about it, you get to say, "Mom, I told you how I felt and I am not going to argue about it." Then change the subject.