Am I wrong for hating crit items/builds?

For Mercury, I would disagree. Crit on Mercury is essential. You will almost always build crit.

"When sould I build crit and when should I build penetration?" - For hunters? Depends on team comp. Also depends on smaller things like attack speed steroids, if you have a steroid you would prefer builds that don't overcap attack speed when your steroid is active, and can also depend on if you're an ability based hunter or not (or a hybrid, like AMC/Hou Yi). But usually you're building crit against squishier comps with less tanks and you're focusing on the enemy adc more than the frontline, you go qins build against tankier comps and avoiding direct boxing with the enemy adc if they're building crit.

"No, Neith doesn’t work with crit" - actually she can, it's just not optimal for her and other hunters can do it better, especially as ability based hunters fall off lategame. Nemesis can work with crit but again not great on her. Of course crit on Loki is a terrible idea.

As Mercury you want crit in 90% of your games. I've seen 1 or 2 pros go a more bruiser build on him with perhaps 1 crit item like Rage (think it was CaptainTwig) but thats about it.

Crit can be viable on certain gods, like the ones you mentioned. I'd guess that people who don't fully understand how building works in Smite just think that since you'll still be basic attacking, giving yourself a bit of chance to do extra damage has to be the right way to go.

When I'm playing with an AA based god like Chiron, oopss, Izanami I build it. But in other situations I also hate it mainly on my Cupid.

I guess people become fascinated when they see that 500 critical hit appearing in their screen :v