>Usually the best argument opposing accessibility is that the authors/developers don’t know what they are doing. When they say accessibility is too expensive that’s what they really mean, and it’s not a good argument.

There's no slippery slope either. If lack of accessibility is just a matter of incompetence and not cost, then there's no downside or cost to adding it everywhere. I don't get the point of not acknowledging that there are costs to accessibility. I get that it's not a good justification in most cases, but there's no benefit in denying that it has costs too. It just discredits the rest of the argument imo.