Think of a big motorway hold up where there has been an accident and the motorway has been closed due to an accident. There will be hundreds if not thousands of vehicles all sat there with their engines running, belching out toxic fumes, soot and particulates into the atmosphere.
The same for every big town and city worldwide during rush hour. 
If every vehicle was equipped with stop/start then this type of pollution would drastically reduced and in my opinion worth the minor inconvenience. 
You can always turn the key off yourself in such circumstances 
People don't though..... 
No, they don't. If it's a hot day, with no breeze, it's murder on the M62 when it clogs.
Start stop auto disables if it can't cool the car, in the hot weather I found just few moments after I stopped it would start again in an aid to keep the air-con going.
Try a Civic. Bloody thing stops at every junction in 35C heat, when you have its piss poor A/C on lowest temp. I sent the first one back, believing both the A/C and the stop/start was faulty, but its replacement was the same.
Granted, that's the worse implementation I've come across though. The Focus I had last month was all too keen to turn off, but single button to quickly disable, which isn't such a hardship.
But why should drivers have to piss about constantly disabling it, just to appease Londoners and other people who want to live in smog infested places. Line the do-gooders up, as normal.
I do believe Alb's Merc *should* have start-stop though, else he'd be craving fish and chips at every junction.