[Someone]

The language outside politics isn’t, but if you start using it as a weapon in politics (“there is a basque language, so there must be a Basque Country”), it can easily become controversial.

That certainly is the case when you start killing people for that cause (https://en.wikipedia.org/wiki/Basque_conflict)

[maze-le]

You do realize that militant Basque nationalist paramilitary groups are disarmed and disbanded since more than 10 years, yes?

It's like saying Irish is controversial because the Provisional IRA existed as an organization in the past...