Peace to everyone,

About two years ago, a friend of mine stumbled upon the path which he claimed would bring him closer to Allah. He started growing a beard and wearing a taqiyah to emulate the Last Prohet (pbuh), began to favor the death penalty for homosexuals (apparently what cannot be corrected, must be killed) and refused to have food over at my place because it's bought with my mother's income which he claims is haram since mum works in the entertainment industry (not the ADULT entertainment industry, mind you).

Fortunately, I recently discovered free-minds.org and it's people who have addressed most of the issues that trouble me regarding Sunni doctrine. So when I suggested to my friend, by citing Quranic verses and certain ridiculous hadiths, that his source of Islamic law may not be as pure and unadulterated as he thinks, he asked me "Well, what proof do you have that the Quran hasn't been tampered with as well?"

What would people hereabouts say to such a question?

P.S. What's the Quran's stance on people working in the entertainment industry?