You family just care about you, that's all. They will see things completely differently from you do, and they have every right to voice their opinion, their concerns. As it is happening to you, there are plenty of things that you wont be seeing that your family does and it will worry them, it worries them even more when you can't see those things for yourself.
I understand that you see it as your body therefore you can do whatever you like with it but your still young, what if you were to regret doing this? It's worth listening to your family when they explain their concerns to you. They aren't doint it for the good of their health, they are doing it for the good of yours. Just because you have had no problems yet, doesn't mean that you wont get any in the future.
You are 17 years old, your whole life ahead of you but look at what Apagg posted above, are those things you are willing to put yourself at risk at? It might not seem it, but it is serious and at your age, it's something you shouldn't be doing in my opinion.
You will keep going until your waist becomes smaller and smaller, it's something that you will never be satisfied with. It seems like already it's starting to become quite serious with you as you are wearing them so often and such. At the end of the day, it's completely up to you what you do but don't just shrug off the advice and warnings your family are giving you. I'm not going to pretend that I know the the health implications, I don't but going on what Apagg said above, I personally wouldn't put myself at any risk of those things, but that decision is left up to you. I think you need to think about this seriously, try and take the views of your family on board and see it from their point of view.