Beautifully put point Paralipomenon.
Obviously Terry is perfectly entitled to an opinion. I can't help but think 'can't happen' is less supportable than 'might happen' and just re-stating an argument and taking no real effort to address the faults in that argument is not going to change that.
Terry, you seem to miss that a sentient observer capable of asking such a question might arise on other planets, and say exactly the same things. Might. To say it can't requires bigger leaps of faith than to say it might.
There probably will be solar systems with planets that can support forms of life that could achieve sentience and develop technology. Such planets are below the limits of observability in other solar systems at this time; we can only 'see' super gas giants today, and I am for the sack of argument excluding any possibility of gas giants developing life with intelligent technology-using societies. Soon we could well prove this point.
Humans exist is just because that's how things turned out. The dominant sentient species with a technological society could have been descendant of marmosets or sea otters, for example. The factors which lead to the development of human sentience could have happened in other species, as they are more to do with sexual selection than survival to be able to breed; it wasn't our environment or specific (as in no others possibly could) ancestery that made us smart, it was what the females found attractive that made us smart. That was just happen-chance; females liking big colourful tails is nothing to do (directly) with fitness to survive - it's a bloody liability - it didn't really help Peacocks become more intelligent. What females pre-humans liked, selected in a mate, made humans become intelligent.
So just as there could be a planet with a guy called Terry ("Slayer of Empires" in T'chakian) with hydrogen peroxide mixed with the water in his body and 7 tentacles saying there isn't any where else life could evolve, a 6' tall marmoset called Terry ("Gatherer of nuts" in Chk!-Chk!--Ch~~~llk!) could be telling his kid that whilst showing them the giant chimps (Pan Terrestalis, one of three species in the Genus Pongo, see P. paniscus and P.troglodytes) at the Zoo.