...We don't attempt to teach nematodes to read!
I work as a substitute elementary school teacher a few days a week. I am not so sure your right about this one...
Why would they WANT to contact humanity?
Maybe they like our art or our comedy or how we look. Perhaps they are fascinated that life like ours could develop so rapidly or maybe they are amazed how incredibly slowly we progress. Possibly we are the greatest entertainers in the known universe. Maybe we are the baddest ass little mercenaries ever to have sprouted from a ball of mud and they want to hire us to do their dirty work. Perhaps the ETs are a civilization evolved from something like a beehive where little value is placed on the individual, or maybe the way we as individuals seem to instinctively band together into tribal nation states is something they have never seen. Perhaps in all the universe they have discovered that the greatest concentration our particular wavelength of brainwaves is right hear on Earth and will solve their energy problems for eternity. I can speculate reasons why they would want to contact us as easily as you can speculate reasons why they would not. None of it matters though because for now it is ALL just speculation.
I'm not confusing resources of any sort. Even assuming that they could exterminate us like cockroaches is silly. Imagine humanity scrapes together the resources and technology and motivation to send out our first interstellar mission. Would we be able to decimate a planet in a day? Maybe, if that's what we'd set out to do, but once again that assumes that we would even have an interest in doing so (and on a lighter note, have you ever tried to kill a cockroach? Relatively speaking killing human beings would be much easier.)
I get your point that you think we are worthless as a species. I just don't see any justification to believe that an alien species would feel the same way. You can't even get close to a consensus about our value as a species right here at home where we share common needs for shelter, food and companionship. I concede that it is possible you are right but only with the stipulation that it is just as possible that every sentient race in the galaxy who has heard our signal is racing here to bow in supplication to our greatness.
There is simply no basis for asserting a conclusion one way or another when you start applying morals and values to the situation.
Anybody intelligent enough to be able to travel throughout this galaxy or beyond, or even just communicate, would certainly study us for awhile. They would have learned by now that we humans are a warlike race that cannot get along with one another even on our own world. Even in our fictionalized scenarios, with imagined technology, such as Star Trek or Star Wars, there is nothing but war and death, such as the destruction of entire planets by some of our imagined technology. Human history provides an absolute guarantee, that if we would meet such an advanced civilization, we would use their technology against them and one another.
Typical that some guilt ridden touchy feely sentiment gets modded insightful here.
The entire premise that some advanced civilization would evaluate humanity on it's ability to get along is ludicrous. Wasn't that the whole storyline of the Q in TNG?
If we are going to start asserting crap like this, then it would be equally valid to suggest that we are the equivalent of the 98 lb. freshman nerd of the universe and that we've been stuffed in our own locker. How about that instead of our galactic neighbors being worried about our 'warlike' nature we have been shunned for being a bunch of weak ass little pussies? Maybe they are just waiting for us to sort out our little squabbles so they can deal with the one with big enough balls to kick the crap out of everyone else. There is NO basis to suggest that either of these scenarios are more or less likely.
I'll buy just about ANY technological explanation before you'll convince me that we are being left alone because some advanced civilization who can hear our signal is essentially scared of dealing with us. Honestly, the suggestion itself is the height of conceit.