Denying that we are in a simulation seems a bit like pre-Galileo conventional wisdom claiming that the Earth was the center of the universe. What is so special about this universe of ours, besides the fact that we're in it?
If a well-financed team of humans could create a simulated "universe" in a computer with sufficient complexity that evolved beings in the simulation exhibit "intelligent" characteristics, then that seems like a good bet that someone could have done that for us. It actually seems much more plausible than the other alternatives. Wait, what are the other alternatives again?