Archer turning a blind eye would only apply if he received their call for help and ignored it. What Archer did was acknowledge their call for help, learn about what was wrong with them and, this is a big one here, DEVELOPED A CURE.At worst he turned a blind eye to assuage his own professional and ethical misgivings and indirectly condemned an entire alien civilization to eventual extinction. He was complicit in the eventual disaster as an observer who refused to become directly involved but not the guilty party that caused that society's demise.
The moment they had the cure was the moment they became a party that's responsible for their demise. Whether this species lived or died was now fully within their power, and Archer's choice was to let Valakians die out.
He refused to help due to a society not being warp capable or ready to join the interstellar community.
And the reasoning behind those factors are what exactly? The Valakians were certainly more developed as a species than Humanity was before they developed warp technology, and they had just come out of their third world war, lived in broken down huts in the mountains and only developed warp technology because some drunk did it because of greed and lust. And what did that do for Humanity in the end?
Troi: It unites humanity in a way no one ever thought possible when they realise they're not alone in the universe. Poverty, disease, war. They'll all be gone within the next fifty years.
Sex and money dude.