The person who said "prison or bullet" for protestors is not a member or spokesperson for the Milei administration, just a legislator in a party in coalition with Milei's party.
I haven't found any actual statement by Milei, just from his administration's Security Minister, who is also not a member of Milei's party, but the one in coalition with his.
The context is a history of protestors shutting down travel in Buenos Aires for long periods of time by blocking roads and trains. (And, one might argue, the Argentinian left's refusal to accept a democratic outcome.)
The Security Minister has said:
- people can protest, but they'll be surveilled, and organizations and individuals will be billed for the security costs of their protests, and
- protestors who block roads may lose public aid.
The propiety of such responses is fair game for debate. I would strongly oppose them in the US, but protests that totally shut down cities are exceptionally rare in this country, and the American left grumbles about losing elections but doesn't demand to retain de facto political control through protests. Plus, their protests are generally for civil rights issues, not economic policies.
So maybe the Argentinian context justifies a somewhat more aggressive government response than I'd approve of here. On the other hand, by taking more aggressive action, the Argentinian government may be setting itself up for an overreaction that hurts its own cause more than helps it. There are both normative and strategic issues at play here.