Lead poisoning, both acute and chronic, was known of as far back as Rome.
http://www2.epa.gov/aboutepa/lead-poisoning-historical-perspective
It's not like they didn't have plenty of warning. LEad paint was known to cause illness and disorders in children in 1904, and specifically linked to ingestion from crib paint in 1914, but it wasn't actually addressed in legislature until 1971.
http://www.toxipedia.org/display/toxipedia/History+of+Lead+Use
Because of altruistic reasons it stuck around in paint? If anything, altruism got it banned!
Lead paint was recommended and preferred for house paint despite being KNOWN to cause illness and injury,
because it was believed to be safer from a public health viewpoint with respect to reducing contagion, and because of its durability.
http://www.leadlawsuits.com/index.php?s=699
That Lead Lawsuit link says that painting was preferred over wallpaper due to contagion issues, not painting with lead paint. Lead paint was preferred by painters due to its durability and ability to absorb lesser amounts of water.
Your link says governments began in the 30s telling parents to watch your children to make certain they don't eat paint chips. Recommended that baby and children furniture not be painted with lead paints.
Your link says the Federal Government suggest lead paint for interiors of buildings because of its
durability. The durability would suggest that it was stay on the walls longer and not chip away. Public education worked in nearly eliminating lead ingestion to non-industry workers. The problem started when poorly maintained homes had the paint chipping away.
So according to your own link, the Government suggested this material because it was a more durable product, not because of disease prevention. Paint, in general was preferred to avoid disease issues related to wallpapers. So this was a quality of the product decision that didn't look down the road long enough (multiple decades), not an issue of an altruistic government.
As I said to Jimmy Higgins, you should perhaps do some research before you dismiss things simply because you don't wish to believe them true, or because they don't fit with your narrative. Whether you think it is "beyond comprehensible" or not, it still actually happened.
Maybe you should read your own research better.