Come now, there are many, many theories that simply offer an idea as an explanation for what is presently observable. It may take a long time to prove the theory right or wrong, but that does not mean that the theory should just be immediately dismissed.
If Captain Caveman had suddenly come out with a theory that water and earth were composed of the same thing on a fundamental level....matter, but we'll call it 'wearth' for purposes of this discussion....at his point in time and level of technology he would have no proof to offer, because the two substances seem to be entirely different on a superficial level. But, on down the timeline we know about matter. So, even though he had not a shred of proof to offer back in the day, as a theory it was at that time as valid as any other. That is the nature of a 'theory.' It does not need proof at the very moment that it is offered.
When you're dealing in the area of scientific study and speculation, that is the nature of a
hypothesis. There's a big difference.
Safe from our behavior does not mean that they necessarily want us to be able to observe what they are doing.
The 1938 broadcast of 'The War of The Worlds' showed how easily people can be influenced into running amok. Heck, even the Denver Broncos winning the Super Bowl spawned a riot.
Maybe they are concerned how the true picture of things would influence human thinking in a negative way at this point in our development.
Prime Directive, perhaps....?
I don't think the theory is such a giant stretch that is completely unworthy of considering.
It's all hypothetical. There is no proof that ancient aliens existed, or that they seeded the earth. There is already a perfectly logical and reasonable explanation, based on scientific evidence, about how life on earth formed. We don't need aliens or gods to turn it into something mysterious or more than the wonder it already is.