I think what most people forget about this issue is that it isn't just a matter of other "intelligent" civilisations, but of whether those civilisations exist "now" - "now" being related to the number of light years the planet concerned is away from earth. Remember just how short a time man has existed on earth - let alone man with the capability of sending radio signals - compared with the total lifetime of the universe. Intelligent life may have existed on planets in other galaxies millions or even billions of years ago; it may develop on some planets in millions or billions of years time. But during the speck of time during which we earthlings are active - I'm not so sure.