The advice is everywhere that you should not mix tires of different tread patterns.

But how come there are no demonstrations of the effects of doing so, like those videos that show the difference between new vs worn tires when driving in the wet?

And what about the majority of us who dont do that

And this is exactly the reason I ask the question:

Why are there no demonstrations showing that this is actually a dangerous practice

Please re-read my question properly ya

tried, tested, proven?

I'm going to have to take your words with a pinch of salt since we dont know the full facts and details regarding your incident