The hate for Comic Sans amongst designers is somewhat confused inside the design community and outside of it too. In my opinion, the issue is not with the font itself, it’s how people use it. You’ve likely seen Comic Sans in places it really doesn’t fit, like this tombstone:

However, that doesn’t mean Comic Sans itself is bad - there are real uses for this font. Firstly, it works great for comics - hence the name Comic Sans. Also, Comic Sans has been proven to be easier to read for those with dyslexia. Since the font has irregular spacing and doesn’t have that many repeating letter shapes, it makes it easier for dyslexics to read. The point is, Comic Sans can be genuinely helpful and used well. A charity called Dyslexia Scotland made a campaign centred around Comic Sans in an effort to create a font that is more professional but still takes the principle design cues that make the font accessible for dyslexics. You should check it out, the design shows how Comic Sans can be used well in design (also here’s a little design from the site to show what I mean): https://www.nothingcomicaboutdyslexia.com/

TL;DR - The hate for Comic Sans is not so much to do with the font itself, but rather how many people use it in inappropriate places (due to Comic Sans being preinstalled on a ton of systems). It’s a lesson on why a basic understanding of font pairing can really improve how well your written words are perceived.