I'm sick of hearing my mother in law say that leaving a baby to cry is good for their lungs, what can I say?

LOL! My MIL and grandma tell me the same thing! I don't believe it is good for their lungs or their emotional stability to cry. The baby crying being good for the lungs is only in the first few days of life when their may be left over amniotic fluid in there. Crying helps to clear it. If your baby is 5 months old, the only thing letting him cry does is teaching him mommy won't be there to meet his needs. I really don't care what my MIL or grandma think about my not so tidy house. I would never be able to continue cleaning with a crying infant in her swing! If she needs me, I am her mom and crying is her only form of communication to me. So that is what I would tell her. :)