Why tabs are evil in ES6?

I have been using tabs till now for all javascript development. But recently I've seen this ES6 style guide which mentions **_"Tabs are evil. Don't use them!"_** at least three times.

I hope there is some rationale behind including this sentence. If there are any scenarios in which using soft tabs instead of hard tabs is superior, a descriptive note (explaining about the reason behind this recommendation) will be helpful. Otherwise, please change the wording, since it makes an impression that using tabs might break something (even some corner-cases).

Thanks!