I cannot or perhaps will not kill them, except for the breeding Netch when they attack...also that one curious quest way up north.
They are among the most beautiful creatures in Vvardenfell.
I've been wanting to ask this question of others here for a very long time.

What say you?

I try so hard not to, but there's something unavoidably hilarious about being a low-level character and throwing a fireball at one, regretting it as soon as it starts shooting poison back, running around working out how on earth to kill it when you can't reach it with a sword, and then the leg-flappy animation when it finally dies...

...I probably need help.

Using a crafting mod that requires Netch Leather for a few things, I do kill one on rare occasions for the leather, while also trapping its soul (Bull Netch fills a Lesser gem).

After the initial surprising experience of finding out what happens when you fire an arrow at one (and somehow MISSING something that's bigger than a house with the second shot), I generally don't go out of my way to pester them.

Haha, I did that exact thing in Ald-Ruhn once XD Good times.

But I do sometimes. My current character's an alchemist, so if I feel I can take something, I'll always kill it for the ingredients.

Don't get me wrong...I'm in no way some kind of animal rights activist. They're just cool to look at, and if I need Netch leather, there are places to buy it in abundance.
I can remember, oh about 10 years ago, attacking a betty netch at about level 2 and getting 'it' inconveniently and helplessly handed to me. They're pretty fierce at low levels.
Bulls are surprisingly pretty weak.