It's the kind of thing that gives philosophers a bad name
While the argument might be valid for absolute knowledge, it certainly isn't true for real world knowledge.
You hear the argument a lot more frequently with regard to morals. BHL has alluded to it a few times. Without God there can be no moral absolutes. Morals must come from a God. Moral exist therefore God exists.
The argument falls apart when no two religious sects can agree on moral standards. Even Christian sects have huge differences and their bible inspired absolute morality changes by the decade.
Dawkins provided an excellent framework for the evolution of morality in
The Selfish Gene over thirty years ago, which neatly explains most of the commonly agreed moral standards - perhaps a little too neatly, but in the subsequent thirty years his hypothesis has stood up quite well.
Beauty is another of these. While 'it is in the eye of the beholder' most people have broad agreement about what is beautiful and what isn't - even across races. Cultures sometimes single out a particular feature and that becomes over emphasised to the point of aberration: the extended necks of Kayan women, bound feet of Chinese women, exaggerated silicone breasts of American women (why is invariably women who suffer under this?) and standards change over time (Rubenesque women versus today's heroin chic)
Similarly there is quite a good broad agreement over what is right and wrong. This changes over time too. I don't worry that my sense of right and wrong is internalised because it seems to be consistent and as long as one group doesn't get to push its moral aberrations on the rest, society functions quite well.