Furthermore, whenever shareholders sell shares after the buyback, their shares are generally worth more, so they pay increased capital gains, too.
I don't know which yields more tax revenue in the long run, but buybacks definitely generate some tax income.
The only time I could see a "buyback" influencing share price without taxation is if the buyback has a price cap, and every shareholder believes that the company is worth more, so they don't sell any shares back. This is exceedingly unlikely unless the company is very thinly traded.
From my perspective, the key difference with a buyback is the winnowing of shareholders to those who believe more-strongly in the company's future. With a dividend, every shareholder gets a small amount of cash. With a buyback, some shareholders get cash for their shares, and every other shareholder gets a bigger slice of a company that is worth less (total) money.
If the market is efficient (and it isn't, but it can be) then following a buyback, one would expect the market capitalization of the company to be smaller, as the company has paid out money. After 6 months, if the market cap of the company, plus the funds expended in the buyback, is greater than the inflation-adjusted pre-buyout market-cap, then the company has created shareholder value through some other mechanism (even if the mechanism is pure psychology).