This is a question of political values and normative judgment rather than an empirical matter I can search my way to an answer for, so let me share some thoughts rather than "facts."
Arguments that NATO has been beneficial:
•It's credibly deterred large-scale war between major powers in Europe for over 75 years, which is historically unusual
•It provided a framework for reconciliation and integration after WWII, helping former adversaries (like Germany) become stable democracies embedded in a security community
•It gave smaller European states security guarantees that arguably let them avoid the kind of great-power domination or forced neutrality that constrained countries like Cold War-era Finland
•It has intervened against ethnic cleansing (e.g., Kosovo/Bosnia in the 1990s), which some see as morally justified
Arguments that it's been harmful or mixed:
•Some argue NATO expansion eastward after the Cold War needlessly antagonized Russia and contributed to current tensions, including arguably the war in Ukraine
•The 2011 Libya intervention is widely seen as having contributed to state collapse and long-term chaos
•Critics on the left often see it as an instrument of U.S./Western hegemony rather than genuine collective defense
•Its out-of-area operations (Afghanistan) had very mixed results relative to costs
•Nuclear deterrence doctrine itself is morally contested — it rests on threats of mass civilian destruction
Where reasonable people disagree:
•Whether deterrence/alliance systems reduce or increase the risk of war
•How much weight to give sovereignty of alliance members vs. the security anxieties of non-members like Russia
•Whether "good" should be judged by outcomes for member states, non-members, or by some universal standard
I'd lean toward saying it's been net stabilizing for its members and for preventing intra-Western European war, while being more genuinely contested and mixed in its effects on wider global stability and in specific interventions. But that's my judgment weighting certain values (state sovereignty, deterrence, democratic solidarity) over others — someone weighting anti-imperialism or non-alignment more heavily could reasonably reach a different conclusion.
What's prompting the question — are you thinking about a specific NATO action, its expansion, or something more philosophical about alliances and power generally? I can dig into specifics if that's more useful than the abstract debate.