Why is mixed content blocked in Safari 9.0.1?

Yes it is pretty annoying. While the old Safari Version was a little bit to loose on this thing. Safari 9.0.1 blocks all content.

I think it is the only browser where you cannot disable it in the developer tools.

It's not merely annoying, it is internet-breaking.

Yes, everybody should be serving all content everywhere over SSL; we know already.
But the fact is that this just isn't how the real Internet is in 2015, and sometimes we don't have the option (or the control) over how content is served.

Now that Safari 9 blocks mixed insecure content and offers no way to work around that behavior (like every other browser does), it means that Safari becomes unusable for certain things.
That doesn't bother me in particular; I hate Safari, to be honest; but we have a lot of Mac-using customers who don't know any better and use Safari blindly because it's what came on the computer, and the mere suggestion that they download and use a different browser is met with the same incredulity as if you'd suggested they try eating a buttered weasel.

There is no solution I've yet found, apart from using a different browser.

Apple has not even acknowledged this change of behavior in Safari, much less weighed in on the issues that have resulted from the change.The fact that there is so little public discussion about it astonishes me.

This is still the case in 9.0.3. I am really surprised there isn't more discussion regarding this by now, or that Apple has not addressed this with a support document of some kind. Does one exist that I have missed? I'm also surprised that no error message is shown when mixed content is blocked. I can find the error logged in the developer error console, but something should be shown to the user in the browser window when mixed content is blocked. Is there a preference to show such a message that I have missed? I am using Chrome now for specific sites that require me to allow mixed content.

What do others think about this issue in general? Should the onus be on web developers for continuing to create sites with mixed content when they shouldn't be? I have yet to find a way to provide this feedback to developers directly on the sites that I use that cause this issue. Regular support channels have also yielded no results, as they are not receiving enough users reporting the issue. Most people will use a different browser, and disable this security measure. Isn't being forced to disable any security measure in order to use an application or site fundamentally wrong? Is Apple taking the high road on this issue, or failing to deal with it?