My dentist said that in 60 years of practice he's never once seen milk sugar (lactose & galactose) damage teeth, and that if anything babies and toddlers who regularly slept with milk tended to have stronger teeth than this who didnt.
You'll find dentists on both sides of the fence.
If you have bad genes, though, nothing but nothing will stop 'mush mouth', (soft baby teeth that rot in the socket), or cavities BUT being as careful as possible (brushing and rinsing every hour) can buy you maybe 6 months.
My husbands family has bad teeth (mush mouth)... But my family has super strong teeth... So we just went with 'an extra few months before pulling and root canals isn't worth the hourly battles. We'll pull them if we need to.
Turns out my son had my teeth... Milk every night (now for 10 years), just like all of us, and gorgeous strong teeth.