[0]https://en.wikipedia.org/wiki/Self-replicating_spacecraft#Vo...
Well that and Spin [2], which probably addresses your point - maybe they're out there and they're already messing with us?
Ultimately, whenever I think about Fermi's Paradox, I am reminded of xkcd [3]. Maybe we just can't tell they're right in front of us.
[1] https://www.amazon.com/Are-Legion-Bob-Bobiverse-Book-ebook/d... [2] https://www.amazon.com/Spin-Robert-Charles-Wilson/dp/0765348... [3] https://xkcd.com/638/
Also, if you okay more StarCraft, you won't be so relaxed about claiming unoccupied resources.
As long as you build your army fast enough to cover them, there's no problem, and you want to be the first to claim those resources.
I do wonder why we exist at all. In that, why hasn't our solar system been consumed by someone else's resource collection process yet.
Maybe we are very lucky. Maybe intelligent life doesn't arise that often. Or maybe it typically self destructs by the time it gets to this point.