Why is 'coasting' bad ?

So, 'coasting' is trained out of you in lessons and is marked against you during the test.

But I'm not fully convinced that coasting is bad in all cases.

My current understanding of why coasting is bad, is three fold.

1: coasting means you are not in complete control of the vehicle, you need to have the transmission engaged in the right/appropriate gear so you can control the vehicle in a split second and give it power to go in a sudden change of direction.

2: it's bad for a gear bearing, for some mechanical reason I don't completely understand.

3: turning whilst coasting is more dangerous, I think because the arc is wider ? Or you have less traction ? I forget why exactly, but certainly it seems to me that you want to be in full control taking a corner and not finding yourself suddenly needing to change gear, so this one is the most obvious to me and I never coast while turning.

Fair enough.

But there are instances where coasting seems 'harmless' to me, if you are fully aware if what you are doing - please educate me, assuming I am wrong.

For example, I am driving along a long stretch of dual carriage way, traffic is heavy but it is moving fast enough to be in 5th gear. Traffic has come to a halt. Now, I know I am going to come to either a complete stop or at least a 1st gear crawl ... Why shouldn't I coast until the car is going slow enough to go directly into 1st gear ? Shifting all the way down, gear by gear, quickly, seems like unnecessary stress on the shifting when I know for a fact I will be going from 5th to 1st ? Coasting seems like less stress on the gearbox in this circumstance ?

Obviously I don't think you should coast as a rule, but there are occasional circumstances where it seems like the far more natural thing to do and, unless my mechanical understanding is off, less stress in the gearbox ....

I'm talking about coasting from 5th to 1st over the course of around 8 seconds with full situational awareness ... Sometimes coasting from 5th to 3rd ...

Please educate me ...