how the hell does relativity justify that the character can be thrown in black hole and survive ?
This is a big question and scientists (physicists) are asking the question that "what will be the fate of an astronaut falling into a black hole?" ,since the concept of general relativistic black holes have arisen. The answer is the astronaut may not survive.
Because of the tidal forces of the black hole which will lead to spaghettification (http://en.wikipedia.org/wiki/Spaghettification) of the astronaut.
Can we theoretically get rid of this spaghettification?
Yes, theoretically, up to some region. For a rotating super massive black hole the separation between singularity and the event horizon is larger and the tidal force is also less compared to other types of black hole. It is not that it would not stretch the astronaut, but the astronaut may have crossed the event horizon before he/she will actually start to experience the extreme stretch of the black hole, as the event horizon is far enough from the singularity. So for a hypothetical rotating super massive black hole the astronaut can cross the event horizon without having much difficulties. Even though the risk is not reduced, inside the black hole the astronaut may be stretched. But there is another frightening thing inside the black hole other than the sphagettification, which is the singularity.
There can be many types of singularities inside a black hole. In the movie's black hole Gargantua there were three singularities inside it; the BKL singularity at the centre of the black hole, if the astronaut hits this singularity he/she will be alternatively stretched and crunched infinitely and may have no hope that he/she can survive. He/she may be teared apart to give atomic or sub-atomic particles but physicist don't know what will be the fate of those atomic or sub-atomic particles. But surely the astronaut is not going to survive, anyway! The other two singularities are the infalling singularity caused by enormous matters that has fallen into the black hole after the astronaut and moves in the same direction that of the astronaut and the other one is outflying singularity caused by the matters that has fallen into the black hole before the astronaut. The image from the book "The science of Interstellar" by Kip Thorne may help to understand(the BKL singularity is not shown in the image and is situated below the outflying singularity),
Now what will happen if the astronaut hits one those singularities. This singularities would stretch the astronaut but by an finite amount (say, it would make the astronaut 1 meter longer and then leave him/her to live a happy life!). Now, will the astronaut survive this finite amount of stretch? May be or may be not. I personally believe the astronaut may not survive, because his/her bones may be broken, there may be internal bleeding, nerves may tear etc. Kip Thorne himself says,
I’m dubious of survival, but we can’t be sure. So I now think it respectable, in science fiction, to posit survival.
But how to survive from the BKL singularity, here comes the concept of putting a tesseract just after outflying singularity and before BKL singularity. See the following image (again from Kip Thorne's book),
I am not going into details about the tesseract here but the tesseract let the Matthew McConaughey's character to get out of the horrible black hole.
So, it is very clear from the above discussion and from the statement of Kip Thorne is that science or General Relativity does not justify that an astronaut can survive after falling into Black hole, but the event is justifiable if you consider the fact that it is a science fiction story.
also if the robot can not send INFORMATION about what is inside the black hole why did you send this to analyze the black hole ?
There is nothing inside a black hole between the singularities and the event horizon. The robot TARS in the movie had struck by the outflying singularity and from that singularity it might have collected some "the quantum data" and that was what the robot sent via Matthew McConaughey's character. That data may be very important to that context. Now, it hadn't collected any data from the BKL singularity, a very different in kind from the outflying one. So the data is very partial and less efficient to manipulate gravity, in my opinion. And more, how did TARS collect the data? Is collecting such sufficient data only by striking the singularity possible? may be some other issues of debate!
and also why they say that a rotating black hole can be transversed ?
I think the word should be 'traversed'. Anyway, I have noted above the reason why the astronaut will be able to cross the event horizon without much difficulties. But this does not save the astronaut scientifically in anyway.
Hope that answers your question.