I too taught my children to behave in public and they were good. If one started to cry for whatever reason, wet diaper, hunger, sick I left so as not to disturb others but mostly to just take care of my baby.
If a child has mental issues things might get a bit stickey and I would hope that people would be more understanding if a child has autism or another form of mental illness. Just because one is not so called perfect does not mean one cannot go out in public.
If I saw a child who had issues crying I would be much more understanding then a child just being a stinker and mom not doing her job.