One argument I run across in evolutionary literature is that cold-blooded species (i.e. fish, reptiles, amphibians) are more primitive than warm-blooded species (i.e. birds, mammals).
Now, as a mammal, it's flattering for me to believe that my species is more advanced than those backward cold-blooded creatures, but in the interests of scientific integrity, I must put aside my chauvinistic speciesism and consider the claim objectively.
This is an example of how the theory of evolution fosters intellectual sloth. Just say the difference is due to the fact that some species are more primitive than others.
A better explanation is the principle of tradeoffs. On the one hand, to be a warm-blooded creatures makes you more adaptable. You aren't so dependent on your surroundings. You can survive and thrive in more ecological zones.
But that comes at a cost. A higher metabolism consumes more energy, which–in turn–requires more frequent food intake. It's easier for warm-blooded animals to starve.
In tropical zones or the ocean, where the temperature is fairly constant, it's more efficient, more cost-effective (energy-wise), for the body temperature of creatures to derive from their environment, rather than having their bodies produce heat. It's a tradeoff between adaptable design and economical design.
Finally, you have cats. These are technically warm-blooded creatures, yet they like to sun themselves behind windows or lie on car hoods to absorb the engine heat. How do we account for that?
The scientific explanation is that cats are the devil's familiars. Although outwardly warm-blooded, they betray their ultimate affinity with the Dragon or the Old Serpent. And that, in turn, accounts for the diabolical disposition of house cats.
In fact, cats have never gotten over the fact that the Egyptians worshiped them as gods.