No, it isn't. People are interested in whether a stock has volatility, and whether it has moved x%. If a $10 stock loses $1 it should show a roughly matching pattern to a $200 stock losing $20. Intersecting at zero will show a very large movement for the $10 stock and a very small movement in the $200 stock, despite the effect being the same to stockholders.

It very much is, because stocks don't start at zero and your entry point will also not be zero. You can be deep in the red long before the stock gets anywhere close to zero. Even when a stock hits zero it doesn't always mean something useful, look at the Hertz bankruptcy for a good example. As far as stocks are concerned, zero is arbitrary and pretty universally a useless reference point.