I don't.

If only 20 widgetshares exists in the world and we each have 50% (you have 10 and I have 10) and the market for widgetshares is $200.

Should you be taxed for your theoretical $5.26 gain if I destroy 1 widgetshare but you haven't sold any. Buy backs are no different. You will pay taxes if you sell.

Personally, I think you should pay taxes if you take out a loan using the market value of the shares as collateral. This is where everything starts getting funny and companies and individuals start being able to avoid taxes forever.