I'm guessing they call it something different where you live, but in America "blind spot" refers to the area you can't see in your mirrors, and must turn your head to see. It's literally what you describe as you talk about a car passing in your second paragraph. "Checking your blind spot" refers to the process of physically turning your head to check and making sure the lane change/turn is safe to do.
The reason he painted you as an invincible road warrior bent on killing pedestrians is because you denied the existence of one of the biggest causes of car-on-non-car incidents: failure to check blind spots. Which, prior to this comment, you definitely sounded like, and I think you'll agree if you reread your comment with the new context of what Americans call "blind spots".
I am American, but I'm trying to get to where the disconnect is.
What I've usually heard referred to as the blind spot is diagonally back, sort of looking out of the back seat windows on either side.
I've driven in a lot of cars where they have their mirrors set up incorrectly, and yes you have to turn all the way around to see that spot.
I'm saying in my cars, with a proper setup, you don't need to turn back that far. You only need to check out your own window, which hardly requires much of a head move.
Turning around and checking backwards takes your eyes completely off the road, and is quite dangerous.
We're saying "you need to check your blind spot when driving" and you're saying "blind spots don't exist, but also you can almost completely eliminate blind spots by mirror position, but also I still check blind spots".
The disconnect is that you've arbitrarily defined "blind spot" incorrectly, and refuse to acknowledge that "the bit of road not shown in rear view mirrors that is only visible by physically turning your head" is a blind spot. No amount of mirror adjusting is going to be able to fully replace checking a blind spot. Even using the method of the video you linked, seeing cars 2 lanes over merging in is basically impossible.
Blind spots are real. Mirrors, by definition, can't show you everything in your blind spot. If you don't check your blind spots, you could be responsible for someone's death.
I feel like you're being the thing you're accusing me of. Don't think we're going to get anywhere, I have nothing new to say. I think a reasonable person can decipher my point of view pretty easily.
I'm just gonna respectfully back out at this point.
This is the image, taken directly from your mirror adjustment video. The red triangles (added by me) show the "blind spots" you have when using just your mirrors, as adjusted in this video. If you fail to check these blind spots before making a driving maneuver, you could easily kill someone. You have to turn your head to check these spaces. The act of turning your head is the literal definition of checking a blind spot.
Feel free to back out of this discussion, but be sure to check your surroundings before going in reverse.