Yes natural selection is in some areas a bad thing.
Do you want blind people to live, deaf people to live, disabled people etc.
Natural selection would kill them quickly
Apart from being obviously untrue in that blind, deaf and disabled people have existed through human history, this ignores the most obvious category of humans that would die if natural selection worked in the rather crude way you portray it, babies.
As to whether the what happens through natural selection as being 'bad', I suggest you need some criteria and justification for them. Got any?