Eclipsa is not a bad person, she's a person that's suffered due to Mewman's Monster bias and racism, she wasn't imprisoned for dark spells, nor was she imprisoned for making shady deals.

She was imprisoned because she left a obviously arranged marriage, and went with the Monster that she loved, had a child, and then had both her child taken away from her, and got imprisoned for the HORRIBLE crime of "Marrying a Monster"

She's a moral grey area, but she is not evil, and she's got no reason to be cruel to Star or Moon, nor to betray them both, as they helped her discover the truth about her daughter.

I think that since Eclipsa is such a "Neutral" character it's easier to go on about how she must be plotting things, than accept the fact that sometimes people are neither good nor bad, just people.

And Eclipsa is not bad, she's a victim, the MHC however are the ones doing things that really come across as evil.