Only one of Eclipsa's spells corrupts magic and is precisely the one you can't read unless you learn high mewman because she knew it was that bad (read the fucking book). The others are average tier at most compared to other chapters in the book. I'd say Skywynne's and Solaria's are the most dangerous by far.
Even Star said it in season 2: "This chapter is no big deal, why are you so paranoid about it?"
Eclipsa was really careful about what spells ended in the book. In the trial she mentions: "I created darker spells but they didn't make it to the final cut for obvious reasons. The key of writing is rewriting"
That's quite responsible if you ask me, considering how much of an airhead she is.
The Darkest Spell itself comes with a warning that it must only be used as a last resource against septarians (only)
MOON ASKED FOR THE SPELL EVEN AFTER ALL THOSE WARNINGS and she would be dead if it wasn't for it. The Darkest Spell saved Mewni from being wiped out by septarians twice so shut the fuck up.
This is not whitewashing, it's just not blaming the the rifle inventor for what people do with them.