i dislike them because honestly, they're kind of dumb and ridiculous. most sparkle-creatures have uncoordinated colors, or are simply too overloaded with colors. i don't like entirely black characters, either, i.e. #000000 black.
if you're going to have a neon character, be low key (and coordinated) about it. i have sparkle-creatures, myself, however they're not magenta with cyan stripes & yellow spots. the worst i have is a charcoal cat with chartreuse eyes, pawpads, eyebrows, and tongue.
however, this is just how i feel about it. some people don't like cherry lollipops, while others do. it's just not my thing, and it's certainly not because i don't like those who are 'different' - that's totally absurd.
edit removed the bit regarding neon colors hurting eyes - forgot about those who wear prescription lenses/those who have vision issues, my bad!!