Well, if the site normally validates, and this time the HTTPS certificate is self-signed all of a sudden - why of course I want to see a big, red, scary warning, because that's what the situation requires.
(Most browsers allow you to exempt specific sites from this warning - this is, however, a significant decrease in security ("to see the dancing hampsters and download our malware, click 'yes yes add exception agree agree I know this is a bad idea yes yes'"); Chrome - aiming to be the browser for the masses - decided to go with the "secure" part of the secure/easy tradeoff.)
(Most browsers allow you to exempt specific sites from this warning - this is, however, a significant decrease in security ("to see the dancing hampsters and download our malware, click 'yes yes add exception agree agree I know this is a bad idea yes yes'"); Chrome - aiming to be the browser for the masses - decided to go with the "secure" part of the secure/easy tradeoff.)