This was brought to me over the question: Why do the changelings feed off of emotions and stuff? The original deceptive predatory nature of the Changeling seemed pointless when the Changelings could have just integrated themselves with the pony society. It's such predatory nature that is the reason why they were feared by ponies in the first place. 

Changelings weren't always, well, Changelings. They were originally known as "Love Bugs," living in conjunction with the ponies. They looked kind of similar to modern Changelings, but without the transformation magic. The appearance of themselves was based upon the reigning monarch of the time. This metamorphosis is reflected in the show when the changeling's change to Thorax's new scheme.

Chrysalis came to power prematurely when the previous queen died of an unknown ailment. Chrysalis was not ready to take over the throne, she was still going through a bit of a rebellious phase. Her appearance was considered by herself to be radical and cool, a feat achieved by her development of disguise magic. She did not see anything scary about it. When she took over, this appearance was forced upon the Love Bugs. The ponies feared these Love Bugs, they did not look cute and cuddly as before, in fact, as far as some ponies were concerned, they were a separate species altogether, they might have gotten rid of the Love Bugs. Chrysalis did not understand this, what was quite so wrong with their current appearance? Apparently, ponies did not share her opinions, but rather than change their appearance, she spread the Transformation magic upon the hive. It would now be standard practice to change their appearance around others, while deep down their appearance was still the same. They were now proper Changelings. And Chrysalis was pleased.

Of course, Changelings weren't perfect, and some of their disguises slipped through. The changelings were discovered, and that made their lives harder. Chrysalis was too stubborn to change themselves. Of course, how could they go back to being Love Bugs anyway, how would anypony believe that? AS far as she was concerned that would never work and she hated it.