:Given that we posted in the same minute I wonder if you read my previous post. I find your tone unfortunate. In future, I'll post suggested changes here if they are substantial. To address the edit again: 
 :* "Thus aliens may be broadcasting evidence of their existence that we are not looking for, or they may not do things that we would expect any technological civilization to do and thus not broadcast the types of evidence we expect." Redundant because mentioned in greater detail later and syntactically awful to boot.  
 :* "We can speculate on possible differences between ourselves and alien species, and try to take these into consideration, but all such efforts may be flawed." A "no shit" sentence that we don't need.