I think this actually illustrates the point people are trying to make, you know your dogs, you know how they like and when left to their own devices they will each choose different ways of dealing with the heat during hotter times, which you let them get on with.
A lot of the dogs I see being dragged around in hot weather in the middle of the day, don't look happy to be doing so, they are head low, tail low, panting, not sniffing, plodding behind the owner, and basically just enduring it, anyone who knows anything about dogs knows when a dog is happy/sad/frightened/excited etc, these are the ones that stand out to me, anyone walking a happy dog, walking ahead, sniffing, head and tail up wouldn't even register on my radar, no matter what the weather was doing.
Imagine your lab, and while he is trying to hide away from the heat saying, no come on it's time for your daily walk no matter what, we always do it at this time of day and today is no different, clipping him on the lead and walking him round hot pavements with no shade etc while he clearly does not like it, but you do it anyway.. this is the sort of mindset people get angry and frustrated seeing.
It shouldn't be rocket science for people to know their dogs and know what is best for them, but for a lot of people their dogs welfare is not their primary or even secondary concern.