Let say that a superior being, something that can and will wipe out humanity ask you and only you if humanity deserves this fate, what would you tell ?  

Let say that he speaks about how destructive we are as beings, about the damage we have already done, about the stupidity, selfishness that motivate us. Let say it even presents you what future damage humanity will do. And finaly let say that there is a red button on the middle of a table, between you and the ultimate being. If you push the red button, the humanity will be wiped out and there will be no survivor, not even you. 

If the superior being succeed at convince you that humanity does not deserve to live no more, and that only you, or him can prevent future damage done to earth and the universe, would you push the red button ? Yes or no ? 

Reminds me a little of the Doctor Who episode Beast Below.

As for the tough decision, I really have no idea... I guess you are asking which is stronger: disgust of humanities atrocities or fear of my own death. I think it would have to be a staggeringly convincing argument that humanity would only ruin the universe for me to sacrifice the race. Certainly at the moment I don't think it would be possible to convince me.

The picture is creepy. Can I watch the episode without any knowledge about the doctor who universe ? This episode have retained my attention and it seems intersting. 

And yes, you have to take into accompt that the being will convince you that we will ruin the universe. 

Yes most of Doctor Who is episodic, (this episode included) though it is useful to know at least a little background behind what Doctor Who is about: that being he is an alien time traveler who has a fondness for humanity & most episodes centre around him saving us from enslavement/destruction at the hands of other alien races, or occasionally from ourselves. Sometimes it involves saving other alien races from humanity too.
I would suggest at least starting the series from the beginning (or American TV normally refers to it as a season). Which isn't too bad as The Beast Below is only episode 2 of 13.

Back to your question: As I said I don't think I could be convinced that way, but if I was to be I guess it depends on what the rest of the universe has to offer. If humanity is only good for destroying what it finds in the universe, but what it finds is only lifeless rocks then I say let humanity live... at least some people will be able to enjoy life.

Though or tough?

If it convinces me? Yes-- but only because I was convinced. CAN it convince me? Well, that would mean killing my daughter. Can't do that. Like Batman said, if you kill someone, you take away all that it ever will be. No chance for redemption.

I won't fall for some alien trickery. No button pressing for me!