It is impossible to know, even remotely, how many animals are destroyed every year in Canada because nobody is keeping track. Conservatively, it is in the hundreds of thousands of animals. The fact is that our shelters are overrun, our rescues are filled to the brim and there is still a continuous stream of animals being born every year in commercial facilities, back yard breeders or are simply "mistakes". We are all part of the problem when we continue to create the demand by supporting this market and we are responsible for the suffering that results when we demand babies when perfectly lovely animals (who were once babies themselves) are waiting earnestly for 'forever' homes.
Most people want puppies and kittens believing that they will be able the "mold" the animal "just the way they want". But, very few of us have the understanding of how to successfully raise a happy, healthy, well-adjusted animal and, more often than not, people simply do not know how much dedicated time and patient effort it involves.
Consequently, young animals who grow into adults often display the very behaviours we were trying to avoid. Often, those poor souls are either discarded or chained out, away from the family, because they lack the social skills to live comfortably in our homes.
Too, animals from commercial sources may appear to have been socialized but, in reality, the little glass enclosure you see in the pet stores is the first interaction they have had with their own kind in a healthy environment. That opportunity to socialize is short-lived when their "marketability" is drastically compromised if they are there for any length of time. Don’t be fooled. These animals you see in pet stores, or brought out from sheds by back yard breeders, are far from a 'sure thing'.
Adopting from a rescue or shelter worker is a—far and away—the person will be honest with you about what you are getting. Good rescues and shelters 'temperament test' the animal and will already know which ones are good with children or who should be with only adults. They are more likely to be aware of any health problems (or the lack of them) first hand and will help you make a far more informed choice about who to bring into your home.
If it is not enough that you are saving a lovely animal's life, then rest assured that a shelter or rescue worker has only the best interests of both you and the animal in mind and not their pocket book or ego.