Tech stocks are getting eye-wateringly expensive. Here are a few examples using their price-to-earnings (P/E) ratio. Tesla: 997x Square: 490x Netflix: 83x Amazon: 73x Zoom: 140x These are all very well-run companies which probably have bright futures ahead of them. But their shares are priced for perfection — as if another 20 years of amazing growth is guaranteed.  And those are just the profitable…