As a species we have a lot of issues that could potentially screw up interplanetary contact. For some perverse reason I find it a fascinating thing to contemplate. Throughout the history of human conquest the religion of the conquerors has been shoved down the throats of the conquered. I have a theory that it may be impossible for an intelligent life to evolve without developing some sort of religion. Obviously I could be wrong, but here is my reasoning:
The way I look at it, the hallmarks of intelligence are the capacities for abstract thought, learning via communication and abstract associations. Without the capacity for abstract thought only instinctive reactions will ever be available. Without the ability to learn via communication every generation will have to learn the same lessons over and over again. Without the ability to form abstract associations it would be difficult for a species to ascertain complex cause/effect relationships. All of these are a necessary part of the process of gathering intelligence and growing in intelligence.
The problem is that each of these can misfire. Abstract thought can result in unwarranted conclusions. An untruth spoken via communications can be believed. Abstract associations give us superstitions about black cats, mirrors, tree nymphs and gods.
I just don't see how it is possible for an intelligent species to evolve through natural processes while avoiding the development of superstitions and religions.
Fortunately I think that as we have developed as a species we are beginning to understand that the ability to tolerate differing beliefs (or the lack of beliefs altogether) leads to greater success in interactions on a global scale. Hopefully before we have to contact other species we will have learned the importance of applying the same level of tolerance to whatever irrational beliefs they may hold. Unless, of course, they do happen to be the intergalactic equivalent of the Jehovah's witnesses. We'd have no choice but to send 'em packing in that case.