All the clans have committed heinous acts, yet the tremere are the most hated

[Grumpy RPG Reviews]

My joking aside, a couple of points.

First, vampires are a race of sociopathic tetchy cannibals. They do not need a reason to hate each other. Hate is their default state.

Second, I suspect the "hate" for the Tremere is something the clan founders passed down through mental powers and through the blood. The surviving and involved clan founders of the Lasombra, Tzimisce, Toreador, Gangrel, Malkavian, Nosferatu and Banu Haqim were all involved in the jyhad. They knew something was going on with Saulot, and then Tremere and Tzimisce but they didn't know what for the most part. They could not or would not act directly against the Tremere as a group of vampires, but they did send out bad vibes.

I am excluding the Cappadocians (and Giovanni) from this because the Cappadocian founder was a nutter and Giovanni were not really a thing yet. The founders of the Ventrue, Brujah, and Ravnos were also uninvolved.

[Father Enoch]

Apologies if I'm just repeating something that's been said a million times, but my impression is that the Tremere are not so much hated as they are feared.

They did something that should not have been able to be done. They "stole" vampirism, from a bloody Antediluvian. And they still have access to some form of sorcery, even if they lost their Hermetic arts. No one in V:tM necessarily "likes" each other (generalization) but Tremere have literally done (or at least appeared to have done) something only the Giovanni has accomplished. And the Giovanni had to be a lot sneakier about it.