Let’s put ourselves in the position that we so often put the fabled alien visitors that the more credulous among us insist are molesting farmers all over the world. If we had the technology and the ability to travel across the vastness of interstellar space, to find intelligent life, and to contact and interact with that life in some way, what is the likelihood that we would assume the role of cryptic spectators? We also usually assume that these aliens would be much smarter than ourselves. What would a smart humanity do in their position? Would we engage in the most important meeting in the history of our species, or would we do something as nonsensical as to periodically flatten crops in the hopes of making a blurry photograph for their newspapers?
[This illogical notion is compounded by the fact that we already know that humans create amazingly intricate crop circles, by themselves, in a few hours (skip to 9:25 for the finished product). It's easy, all you need is some rope, a plank of wood, and some knowledge of geometry.]
When we turn the question on its head, the notion of mysterious alien visitors is laughable (it’s apparently not enough that there is no evidence of any visitation to suspend belief). If you chuckled at the graphic above, you recognize this.