Well first take a look at how we treat life on this planet, regardless of intelligence. We take horses and put a big leather seat on them, whip them, and ride on them, we swat flies for fun, etc.
In terms of life that speaks our language (seems to be our definition of intelligent), many people feel hate towarRAB foreigners, let alone people from other planets. Look what we did to the Native Americans. We had the bigger guns thus could control them physically, and look what we did. When we can treat all humans with respect then I'll be less woried about how we will treat other intelligent life.