I think you’re probably saying that’s what an Opinion article is for.

Correct.

But a news article that doesn’t state its biases is not unbiased. And I haven’t seen any news articles where bias is stated.

True, no human produced piece of writing can ever be truly free of bias.

That said:

Normal news article: Best effort of not applying your biases and just reporting raw facts.
Opinion news article: Intentionally applying bias to contextualise the raw facts.

That's all there is in this distinction, but that's nonetheless important I would say.

I don’t know what ‘an environmentalist’ is - as discussed, the news made it up. But as one, would you please define it and explain your bias, y’know, like a news reporter would?

As per: http://dict.org/bin/Dict?Form=Dict2&Database=*&Query=environmentalist

1 definition found for environmentalist

From WordNet (r) 3.0 (2006) :

environmentalist
n 1: someone who works to protect the environment from destruction or pollution [syn: environmentalist, conservationist]

My bias is that I have been hearing from reputable sources that we are destroying or at the very least damaging the ecosystems that supports our species for all of my conscious life. Literally all of it. Doing so seems like a bad idea.

By the way, today I learned there is apparently an older application of this term in the nature-vs-nurture debate amongst anthropologists for people who favour the nurture side of the argument (n2): https://en.wiktionary.org/wiki/environmentalist

Anyway, people make up new words when they need them, I still don't understand the confusion...

Mmmnnoo, they didn’t say. You’re suggesting they would? Or that that is normally done?

No, I'm saying they wouldn't self-identify as such unless it's an opinion piece, because that would be introducing bias into their articles instead of reporting on the facts.