I thought up something for the changelings to make them and Chrysalis more morally gray: the changelings do feed on love but they do it because it's all they can feed on, not because they're trying to be evil. They also tried to reach out to ponies in the past but were rejected for how they looked, the ponies even making them out to be monsters. Eventually Chrysalis decided 'Then Let Us Be Evil' and attacked Canterlot.

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sounds like this would work and it would also give Chrysalis a good reason to attack rather than having her just show up like she did in the episode.

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Chrysalis: Well, you won. Kick us out, tell us we'll never win and then tell the story of how you perfect ponies foiled the big bad bugs.
Also maybe some of the ponies would say some pretty nasty things about the changelings and maybe even attacking them after the changelings officially surrender.

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we have already seen that the ponies don't trust the changelings in the episode where Spike befriends Thorax each of the crystal ponies wanted to thrash that little bug pony simply because he looked different and didn't act the same as them.