While your friend is right, the valuations we're seeing now *should* be low in a couple of years, IMHO your friend is missing a very key point. Stock prices are not determined on valuations, they're determined on the number of buyers and sellers. Valuations are a great guide in a stable market, but when the market is in a downward spiral, as it is now, people are selling stocks and shorting stocks irrationally. This market will have a bottom, and it is not 8000, that much is for certain.
Look at it this way:
You own 100 shares of a fund that mirrors the DOW that you bought for 13 dollars a share when the DOW was 13000. Now your 13000 is worth 8000. Well, if the market drops to 5000, that's how much your investment is worth. However, if you sell now, at 8000 and buy back in at 5000, you're getting more than 50% more shares, and when the market pops back up, your profit will be that much sweeter. Just some food for thought.