Sometimes I downshift some times I coast to a stop then shift down to 1st. To me it is no big deal either way. My Roadsmith conversion has full sized car U-joints and a Ford car diff. I don't worry a great deal about abusing any of the components.
I have done Run For The Wall 3 times (that's enough for me) while on the ride they tell all riders to not use their brakes. You are supposed to downshift under all circumstances. My response was a resounding screw you, breaks are too important to not use in a mass migration like that. They say that if you just touch your brakes it causes your brake light to come on and that confuses the riders behind you and then they hit their brakes.
Anyway I think that was a little much to ask of riders. And as for downshifting or not, it's like voting do what you want. If it breaks it breaks if it doesn't ride on.
Personally, I am not comfortable driving behind a person in car or bike that is downshifting. It's hard to tell if they are slowing down and sometimes it's too late. Brake lights are there to tell the person behind them that you are slowing or stopping.
I find it amazing with some of these organizations or benefit rides you go on how unsafe they can be to ride with. A few years ago I rode with the Blue Angels and once we pulled off on a rest stop with about 10 bikes once finished the tail gunner actually drove his bike into the right lane, blocking traffic and then waved the bikes on to get on the merge lane. Scarred the crap out of me. This was on I-75 in South Florida with a speed limit of 70. Needless to say I never rode with them again.
Actually as I write this I am getting ready to leave and take a Trike Riding Course put on by our GWRRA District. It's a 6 hour (3 classroom & 3 riding) safety course. Never can learn too much...