NATO has shown at least some willingness to fight wars of aggression. It's hard to paint the intervention in Yugoslavia in the 1990s as defence of an alliance member, however justified it might have been by humanitarian concerns.
Here is the actual treaty:
https://www.nato.int/cps/en/natolive/official_texts_17120.ht...
Article 4 is quite deliberately vaguely worded. And the treaty also explains why NATO only got involved in Libya after the UN requested it to.
Even the Yugoslavian war did not - though it almost happened - ended up pitting NATO against Russia, and I believe that if Russia had followed through on the reforms instead of turning into a Dictatorship/kleptocracy that they just might have joined NATO at some point.