> A certain percentage of humans will never acknowledge that machines can be intelligent.

Doesn't this assume there IS an objective, quantifiable definition of an "intelligent machine" that is agreed upon by most people? That instead sounds rather subjective to my ears.

Even failing a single unified definition, every reasonable person should be able to define some subjective line of their own.

Some people don't even have a subjective definition though. They'll continue to deny the machines are intelligent no matter where the line is drawn.

It's not worth debating those folks because to them it is a matter of faith and no amount of reason can convince the unreasonable.