The idea of lithopanspermia - that rocks expelled into space from Earth during a dinosaur-killer sized impact could reach another planets surface with viable microbes within them - has also been investigated in some depth. The impression I get is that, due to the body of evidence accumulated, lithopanspermia is regarded as being mainstream, plausible, and worth pursueing, if unlikely. The findings of what I read (some time ago) IIRC were that, while the odds of any single microbe making the trip intact were very bad, they were not so bad as to guaruntee wiping out all of a large population of rock dwelling microbes.
The case of a 1 meter rock ejected from the dinosaure impact was the most commonly used. It was found (again IIRC) to be possible that many such rocks could be ejected into space without being heated all the way through, that the time for space radiation to sterilise the entire rock was tens to hundreds of thousands of years (long enough that an interplanetary crossing might realistically occur), and that landing might be survivable, particularly if the rock broke up as it hit the target planets upper atmosphere. It was suggested that the idea was far more plausible early in the Earths history when many impacts that size or bigger took place - more throws of the dice in effect. I'll try to find the papers.
In space PR and Politics are as important as engineering and science. And no-one can hear you screaming about it.
"There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy."
Exploring other worlds with people is a great idea, but look at what has happened since the end of Apollo: How much could unmanned exploration (and astronomy) have discovered with all that money blown on paper rockets?