National Security Adviser Michael Flynn resigned after the FBI or NSA revealed that he talked to the Russian ambassador about economic sanctions prior to President Trump being sworn in.
He reportedly asked the Russian ambassador to ask his government hold back on retaliating against President Obama’s economic sanctions because the Trump administration would have a new policy.
President Obama’s actions, taken during his lame-duck period, could have put Russia and the USA on a path of tit-for-tat retaliation that would have made it harder from the Trump administration to improve U.S.-Russian relations later on.
De-escalating was a good thing, not a bad thing.
I agree that General Flynn was not a good choice for the post of national security adviser. He was evidently a brave and honorable commander in the field, but he did not function well at headquarters, for which reason he was fired by President Barack Obama as head of the Defense Intelligence Agency.
He thinks the West is in a war with the whole Islamic world, not just the Islamic State (ISIS), Al Qaeda and their sympathizers. He is a war hawk regarding Iran. He would have been likely to get the United States into pointless wars—just not a pointless war with Russia.
I would consider his departure, in and of itself, a good thing, but for the fact that he will almost certainly be replaced by someone else just as bad or maybe worse.
The problem is that he was forced out for (1) trying to stop the slide toward military confrontation with Russia, and that the forcing out was done (2) by intelligence agencies with policy agendas different from the White House.