Tell them that you will only add people you know in-real life, and that if they hack you, or whatever, your parents can beat up their parents. Also, you can't get hacked unless you share contact details with someone, which gives them your IP address, which permits (not legally) DDOS'ing. From there on, add everyone and just rename them to names of people your parents know you know irl, and put their Minecraft name in brackets. E.g. If you added someone called IH4ck3rz on Skype, name them "Freddy | IH4ck3rz", then your parents think that Freddy has a weird Minecraft name, and you know who Freddy, the one in your contacts list, actually is. I do this, although I don't rename people due to me being too lazy, and the fact that I don't share computers means my parents don't check.
Another way is to install a virus on your parents' computer, but one that you can uninstall comfortably, and then tell them that you'll fix it for them when they cry that their computer is telling them to switch off Google Chrome, or whatever. When your parents sigh in exasperation and ask you to fix it for them, do so calmly, and then, after they check, ask for Skype. Having just performed the extraordinary deed that you have, your parents will think in their minuscule brains, "son>hacker", and let you get Skype. If your parents have not yet evolved to a stage of such complicated thought process, and still think, "hacker=son", then you might need to say stuff like, I will only add my friends, and follow some of the above steps.
If your parents still don't let you have Skype, kill them with fire. Might work.