Things we once accepted as totally normal, but we now realize are very harmful:
Slavery
DDT
Driving without seatbelts for yourself or the kids
Not letting women vote
Smoking tobacco
Playing with drops of Mercury
Trusting celibate male priests to watch the kids
Things we now accept as normal, but future generations will find appalling:
The fossil-fuel burning economy
The ubiquity of single-use plastics
Prescribing heroin-strength pain pills like crazy with no precautions against addiction
Citizens of wealthy countries dying of treatable diseases because health care is prohibitively expensive
The cavalier use of synthetic fertilizers, herbicides, and pesticides
The expectation of never-ending fast growth of populations and economies
Eating animals
The insanely high risk of dying in a car accident
Expecting men to wear suits in summer and women to wear skirts in winter
The USA still not using the metric system in 2019