By your own admission, it would be quite a damaging allegation that Letterman inserted laughter digitally -- it would, in your words, 'expose him as a fraud.' In recent years, even NBA teams were criticized for blasting canned crowd noise in sports arenas during televised games. If someone credible actually came forward and said that what your friends suspect -- not "know" -- about canned Letterman laughter was true, that would be a scandal. A scandal that would hit the pages of Daily Variety, Entertainment Weekly, TV Guide, The Hollywood Reporter, Broadcasting and Cable, Zap2it.com, and Drudge Report.
Go crawl back under the rock you came from. Letterman's an unfunny, second-rate comedian and he understandably draws morons like yourself; it's like flies on sh*t.
Good lord, man, you sure have worked yourself into a lather about a guy you've never met and only effects your life if you let him.
Get over yourself! Have another shot of your namesake, pass out on the floor, come to, mop up your puke, and take a nap. Maybe you'll feel better, but I doubt it.