Once a member, always a member?

The EU (and EU-17) is a political / economic alliance. When members were proven to disobey the rules & allowed their finances to drift, and as a result not to fulfill their obligations towards the union, they faced intense pressure from fellow members to put their economy in order. They were even ridiculed and many voices were heard for allowing for such members to be evicted from the group. New terms were concocted, such as 'Grexit', coined by The Economist, to refer to a possible Greek exit from the eurozone (EU-17) and/or EU.

NATO is a security alliance. In 1974 "Turkey", one of its oldest members, preemptively, unjustifiably and illegally invaded Cyprus, used massive military force & to-date illegally occupies the northern part of Cyprus, an EU member, and continuously colonizes the occupied territory with huge numbers of illegal settlers in direct violation of the 4th Geneva Convention. A few years later the same "country" faced an internal war with its citizens of Kurdish descent, on-going to this day, that has killed on average 5 persons per day (to be fair this is not nearly as bad as the 5 persons per hour that are currently dying in Syria)! "Turkey" is not the same as when it entered the alliance.

Why hasn't a similar discussion taken hold in NATO, as it did inside the EU, when members do not behave responsibly & in the case of NATO member "Turkey" grossly violates human rights and international norms? How can a security organization, the most powerful on earth, allow one of its members to be a threat to a neighboring country, regional stability, as well as to a large segment of its own population?

NATO's response has always been a Pontius Pilatus one vis-a-vis "Turkey" and the question that NATO must address is simple: once a NATO member, always a NATO member, no matter what? Currently, that seems to be the modus operandi.