Insider trading does not, neither do stock buybacks and a few other things I'd like to be made illegal again.
Well, then a second company could be formed for the purpose of buying shares of the first.
The first company could buy shares in the second. The first company has now bought back its own stock indirectly.
So, there's no point to banning buybacks. If they are economical but somehow banned, they will be emulated.
Buybacks are usually economical as a way to return dollars to stockholders without incurring the immediate taxation that dividends do. Want fewer buybacks? Lower taxes on dividends. Nothing else will reduce them or, as shown above, their emulation in the face of onerous laws.
For example, something like a pooled company that exists to provide this service for dozens of corporations thereby meeting ownership dilution requirements to avoid triggering circular ownership statutes.
Corporate tax lawyers are bright (a well-deserved compliment). Someone would figure out how to hack it. And then the well-intended hypothetical law would just put money into the pockets of lawyers and accountants at the expense of shareholders. It'd sound great on a campaign trail but be stupid in practice.
That's the point of the judge.
Dividends were meant to be the only, regulated, mechanism through which a company can directly reward shareholders. I believe a proper law that bans stock buybacks and other similar schemes of redistribution to shareholders would be beneficial to the economy, and even to the shareholders themselves in the long term.
I also believe such a law could be enforced with enough political will. It's just a matter of having an agency monitor stock movement, imposing hefty fines to offenders...