To say it bluntly: Sometimes girls are neglected until they die or killed outright.

I think selective abortion is more common then selective infanticide.

Abandonment is common too. My sister worked part-time in an orphanage in Xian for a year and saw a lot of sad things.

Right. And to call this "single child policy" is a nasty euphemism.

Actually, that's incorrect. There's a strong social prestige incentive for your one child to be a boy rather than a girl. There's a strong economic incentive for you to have a girl: there's a tradition of reversed dowries in China, and girls are rare, so the benefits are high.

I thought the reason they wanted boys was that they were the ones who had the means to support their parents in old age?

Perhaps that was the historical reason boys are high prestige, but modern China has huge opportunities for women (who "Hold up half the sky", as Mao put it).

China was a society of prima genitor, like Europe; boys are high prestige because they carry on your family name. All praise to the eldest son!

People who kill their own daughters for "economic" reasons stretch my ability to be non-judgmental.

Infanticide for "economic" reasons is an evolutionary adaptation common in many mammals, including humans, including in rich societies. In the US, it usually gets classified as SIDS.

I'm yet to see a convincing argument for why it's unethical.

Isn't SIDS when a baby suffocates because they are sleeping on their stomach or in a room with poor ventilation? Or are you saying it isn't as sudden and accidental as we are led to believe?

Not always accidental, apparently. Wikipedia has references.

Also, in the Netherlands, child euthanasia is openly practiced.

http://www.google.com/search?q=netherlands+euthanasia+child

280,000 hits.

Do you judge sexual abstainers?

http://www.google.com/search?q=%22abstinence+is+murder%22