I understood the "close to the speed of light" really meant something much much smaller than 0.1c, since on cosmological timescales the difference between the first radio signals and domination from an alien civilization could be millions of years, and that'd still be an instant compared to the time before and after the event. So I'm assuming for the fermi paradox to work out here, we'd not need speeds anywhere near 0.1c
If you move slower than 0.1c then you can’t really cross between galaxies (or at least you are limited to very nearby ones). So we only have to worry about grabby aliens in our galaxy AND we can be fairly certain that there are currently none! Since we ourselves are probably only thousands of years from being grabby this implies we don’t have advanced competitors .This is a very different picture from what Hansen discusses.
0.1c isn't slow enough to solve the empirical puzzle that we don't now see alien volumes. That is the fact that pushes for higher speeds in our analysis.
