Your concern is valid and I am sure it will be dismissed as nothing to worry about because 'cry it out' is a popular method to get children to sleep and it sure works becuase it focuses just on one thing- get a child to sleep. It is not the length of crying time that matters, what matters is the internal happiness. Crying for a minute or one hour may have same impact on the inner well being. Some kids may learn quickly to believe that no one is coming to tend to them or some may keep their hope alive for longer time. Eventually, they all give in.
I highly suggest reading Addicted to Unhappiness by Martha and William Piper. They also wrote Smart Love. Both books offer great insight into what happens to a children's emotional health when we do not attend to their needs. According to these and many other writers/psychologists on the subject of happiness and emotional intelligence, when kids are left crying to sleep, they believe that this is what parents want for them - to be unhappy. They confuse this as ‘happiness ‘desired by parents. Children come into this world with three genuine wishes – To love, to be loved, and feel valued. Children strongly believe that they are causing their parents to love them and want to do anything to please their parents. However, at the same time, they also genuinely wish for unconditional parental love and attention. With this conflicting wish to seek love and please parents, they subconsciously continue to create unhappy situations throughout their life.
A child sleep trained by ‘crying it out’ may seem normal but may not be happy internally, just a compliant child. The unhappiness comes later in the form of night terrors, sleep walking, bedwetting, nail biting, thumb sucking, and many other such ways children learn to soothe themselves when their needs are not attended to and when they don't feel safe and secure. There are many cultures in the world where kids are not ‘trained’ to sleep but still sleep and are healthy with parental closeness and warmth always available to them.
Best,
-Rachna