I think one of the big things many 'mainstreams' fail to think about is that the evolution of technology is not necessarily a static evolution. It doesn't always have to be bronze > iron > industrial. That was *our* particular evolution. "Ancient Technology" could have had a completely different path in terms of being "advanced". I'm not saying I believe that there was/wasn't ancient high technology, but I do believe that it would be close minded of me to shut out the idea, or possibility that if there were humans prior to when we believe civilization to start (Mesopotamia), that they had the same exact technology has us. Assuming they were advanced, doesn't mean they had to have phones or the internet to qualify. I think that's where many get hung up.
Our evolution of technology as anything is built upon its predecessors. So if there was some sort of cataclysm 12,000 years ago or whatever (which is proposed by many mainstream scientists), it's possible that it wiped out nearly all those that were scientists, engineers, etc. of that era. Imagine if there was a global cataclysm tomorrow, and 90% of the population was eradicated. Most of us aren't engineers and scientists. Recreating an electrical grid, even cooking, hunting or building a fire would kill most of the remaining survivors. Unless you hang out w/ extremely well rounded survivalist type people, the basic idea of drinking clean water following a catastrophe would likely be the last of many peoples concerns, killing many. it's not hard to imagine a complete loss of technology following a cataclysm if your first and most necessary course of action is survival.
tl;dr - don't think aliens created the pyramids, Petra or other historic sites, but i wouldn't rule out and remain open to the possibility of a different evolution in technology prior to the dynastic period using sound, or something else as a main proponent.