Earlier quoted context omitted.
Altruistically, it trains users that it is ok, which it isn't. Selfishly, the author really does not want to be storing or even handling these kinds of credentials. It makes them a very juicy target for all kinds of bad actors. Imagine finding yourself in the middle of some kind of account hijacking nightmare that you have unwittingly enabled, having to deal with people who trusted you and have lost access to their a…
You didn't read https://invidio.us/privacy
The privacy policy of not storing passwords is nice but what about when they get hacked and the site starts uploading passwords to some attacker's website?