> Please, tell me the reasons why zooming on a legible, usable design is necessary
Because what is "legible, usable" to most users still isn't to some. Not all of us have good eyesight. Some of us have horrendous eyesight. You may think that 16pt text is "legible", but for some users, nothing less than 32pt is readable.
Because what is "legible, usable" to most users still isn't to some. Not all of us have good eyesight. Some of us have horrendous eyesight. You may think that 16pt text is "legible", but for some users, nothing less than 32pt is readable.
Don't be hostile to those people.