The purchase of 10000 shares of company X, or even the outright purchase of a corner bicycle shop, could very well be considered "consumption". Granted this class of "consumption" could be given special tax status (much like capital gains already does) due to the risk inherent and the general societal desire to encourage this kind of investment. Profit would be gravy if we no longer tax income, and losses could be weighted against future purchases to lower tax burden. It could actually work, but we'd still be arguing over the same old stuff. How much should the rate be set at? Should there be different tax rates for different amounts of annual stock/bond purchases? Should the tax rate be different for private vs. public company purchases? What if you sold shares immediately after a purchase and took a loss? SHould you get refunded your tax, as if you returned a shirt to the Gap? Sould you still get to use that loss as a weight against a future purchase? But that might encourage short-term trading and micro-trading, which is probably not what anybody wants... I could go on.
So in the end, it might be just as complex, and a long and complicated form for anyone who has non-trivial finances might still be necessary. It's why I'm generally against changing everything to a federal sales/consumption tax. It would certainly change things, and it could very well work, but I'm not sure it would actually make much difference in the end.