By convicting Trump for his clear crimes, the USA joins other developed democracies in ensuring its heads of state are not above the law.
Since 2000 at least 76 nations have jailed/prosecuted leaders after they left office—including allies like France, Israel, Taiwan, & S Korea.
Also, SCOTUS can’t grant Trump immunity from this conviction, nor can a future President, because Trump has been convinced in state court, and if there’s one thing Republicans love, it’s state’s rights.