We know that before us there were dinosaurs who ruled for billions of years, which are reptilian. Boom goes the asteroid dynamite, and mammals start their reign. Billions of years later, here we are.
But what if evolution follows a pattern of sorts, and "reptilian" is always the starting point as life moves from water to land? In that case, there would be planets which didn't have a global extinction event that reset and altered the evolutionary path, allowing the reptilian life on those planets a billions-years head start on evolution and advancement. Assuming that intelligence is a large factor in evolutionary advancement, that would put a reptilian species significantly ahead of us technologically. So much so that they wouldn't have an issue using their advanced technologies to fully disguise themselves and integrate into our societies for study or whatever other purposes.
In conclusion, there are likely reptilian aliens living among us. Could be a colleague or neighbor, or that guy you've always referred to as "uncle" even though he's not related to you. Regardless of who they are, I doubt they came all this way to do us harm. That'd be like a Canadian traveling to Australia for the sole purpose of destroying an anthill. Whatever resources we can think of that they would want from us will have been long since solved by them (if they have FTL travel, they'll have molecular printers/replicators). The only unique thing we have is our humanity, and wiping us out defeats the purpose.
The aliens that are here are here for either scientific purposes, or were entertaining enough to be a tourist destination.
Also, we may be the only planet with nachos, so we're undoubtedly going to attract every corner of the universe.
