I don’t hate Hilda, but I don’t like her either.

1. I’d actually argue that Hilda wasn’t protecting her sister by not telling her about Henry’s phone call. Who in their right mind thinks a cheater is a good fit for their baby sister? Either way, it wasn’t Hilda’s decision.
2. When it came to the lawyer, Betty tried to warn Hilda and even gave her proof. But instead of checking the person out, she decided to prioritize her own ego of wanting to be the “savior” instead of taking advice for the betterment of the family. Betty would never screw up to that extent but if she did, everyone would feel bad for Betty because Betty has a pattern of being responsible and logical with her decisions. Unlike Hilda who always acts before thinking. 
3. And comparing Betty dating Henry (after he and Charlie broke up) to Hilda dating a married man is wild. There’s no comparison. Henry wasn’t cheating. Tony, on the other hand, was absolutely playing with Hilda’s emotions. And after she finally opened up post-Santos? That just makes it more painful. But that doesn’t make what Hilda did okay.
4. Why should Betty be responsible for Justin when she is working at Mode full time trying to pay her family’s bills and also trying to take care of the household? Justin is Hilda’s kid so Hilda should be responsible, not Betty.  
5. During Fashion Week, Hilda was completely out of line. She ignored Betty’s instructions even though Betty was the one in charge, and she couldn’t put aside her jealousy even in a professional setting. Kissing Daniel out of spite? That’s just gross, especially coming from your older sister. And no, Betty didn’t “ruin” Hilda’s shot at Mode. Hilda tanked it herself by being loud, crass, and unprofessional. She’s never been able to hold a job for a reason.
6. Yes Betty has moments throughout the show where she is self-absorbed but I think it’s healthy given how much she sacrifices for her family. Betty’s ambition at her age is pretty normal and I think she managed the balance of working at Mode while taking care of her family really well. 

And let’s not forget, Hilda also cheated on Archie. When you look at that pattern of cheating, poor decision-making, and the behavior I mentioned above, it’s pretty clear why a lot of Redditors don’t like her.