Aren't we keeping the fish in an aquarium? So, didn't you just kill your own argument...?
No. A longer life does not equate a better life. Longer life is more appealing to someone with an aquarium because, well, the fish is alive longer. That is it.
You can keep frogs alive almost twice as long by lowering their temperature - but they lose out on activity, do not mate, and don't grow as much. People wouldn't do this with frogs as the difference is more obvious...
However, when it comes to fish, it is alright to give them a less natural life (year round low temperatures) instead of a more natural pattern of seasonal fluctuation because it keeps them alive longer.
You can also keep dogs and cats alive longer by feeding them a very very low calorie diet (near starving) and providing daily stress to stimulate survival responses. It has also been shown that horses kept indoors have a longer lifespan than those allowed to romp in fields and enjoy themselves. But would you do this? Fish fall closer to decoration than pet - especially when it comes to very small schoaling fish like the WCMM - so a long life tends to be favored over a natural and healthy life for the fish.
I have never suggested it would be good to keep them at a high temperature year round. What I am saying is that a high temperature year round is not going to be any worse than a low temperature year round because they live in a seasonal environment. The optimal is a set up where the temperature fluctuates with the seasons - low in winter, high in summer.
I will stick with Chinese (their native country) and Japanese breeding information on them. I take the same stance with goldfish - all the western information says they need to be in low temperature tanks all the time... When the actual breeders in China and Japan breed them in tanks that fluctuate with the seasons, going up to around 30C in the summer.