I see your point, but defense seems wholly unnecessary. In what possible scenario would Greenland be invaded and not be protected by the US, Canada, and/or the UK.
If Russia put down a commercial landing and started drilling off Greenland, we’d throw around sanctions but I’d sure as hell want to see a military base before I’d advocate going to war with a superpower over fewer than 60,000 people. Especially if a decent fraction of the population could, reasonably, claim they were free riding on our blood and money.