how to delete extensions Youku, Tudou, etc...

I agree with you. A customer should not be required to keep these third-party extensions installed on their machines if they decide they want to disable them and want nothing to do with them. The advice provided may be sound but it does not address the crux of the issue. For what it's worth, I've sent feedback regarding this matter to Apple even though it's obviously just a drop in the bucket. And while Apple may not officially monitor these discussions the input and opinions provided here serve a useful purpose as motivation to other customers who agree, to send feedback as well.