I think the author fails to realize whether saying 'easy' is okay or not really depends on what background your audiences have. For example, in the math class I find the professor saying 'it is trivial to get B from A' is quite okay if the proof of that deduction is something the students have learnt in the lower-level classes. I don't know another way to skip the easy proof without saying it is easy.

If you know how well the person you are talking to know the material you are talking about, then I don't find calling the thing 'easy' is humiliating at all, instead it is a effective way to say "no worries, just do XXX and you are good". A rule of thumb is when you are not sure if it is appropriate to call something easy, just ask the person you are talking to whether he knows that thing. Why stopping using the word 'easy' when we are sure all parties of the conversation gets what you are talking about and think it is indeed easy?