In one sentence, this guy blows up his own argument:

"Language is the conveyor of culture."

The way to keep a language thriving is for more and more people to use it, not restrict it to a select few anointed ones. The very reason most first nations and other indigenous languages are dying is because the elders who know the language are dying. If you don't share and remix and renew language and culture, it dies off. Happens all the time.
Can you imagine someone saying "stop stealing Greek stories, or English stories or Chinese or Indian stories"? What would we have, culturally? Zip.

So "steal" away (I'll repeat my position that culture can't be (mis)appropriated because it is collectively owned by everyone.)