Making it equally hostile to everyone is not necessarily a better alternative.
It's possible to design colour schemes that are suitable for colourblind users. Going colourless is not the only solution.
> You should always design your icons in a way that an outline is a good indicator and that a greyscale version works too
Unfortunately designers don't always do this - even supposed design-centric stalwarts like Apple screw this up. The icons in the Mail app for macOS always make me end up spending a fraction of second figuring out which one is which (new mail vs get mail, and archive vs trash vs junk).