It's worth pointing out that the universe, being vastly old, may well have already hosted civilizations on planets whose stars have since turned into red giants and engulfed them - just like our star will engulf us in due course. Again there may be places where life is developing but is not sufficiently advance yet for us to see anything from it.
Then again, anything that SETI picks up is history by the time it is received. Our nearest star is 4 light years away so we are only observing what it was like 4 years ago. We have been looking much, much further back in time but, of course, have not seen what is happening today so we may not be able to know if there are other civilisations out there.
Finally, we are hoping, with SETI, to pick up radio signals that are broadcast from other worlds yet another world might not be broadcasting to us. Sure they may have been like us 50 years ago when lots of radio signals got into space and beyond but there days, with low power FM and Digital stations and the increasing us of satellite broadcasting, very little radio signal gets into space so anyone looking for us from another world would not pick us up now yet I think we are here! So with time a big factor, together with the possibility of radio signals escaping another world it could well be that we might just not have the possibility of knowing if there are other civilisations out there but that is not the same as saying there are none.
I stick to the hard evidence. I only read sci-fi for amusement.