Reason why aliens hide from us? (If there are aliens, that is.)?

i humans are violent and kill each other why would we not kill them ? we use all of our resources and don't care if we ruin the planet for any one else ,we are not able to handle the TECHNOLOGY with out killing every thing we contacted out side our universe we smell; and are ugly to them we are just a pet to be studied it is a law of the universe that more intelligent beings cannot intervene with the Evolution of a lower species as it could interrupt the evolution of the whole space time continuum