. . . burning everyone who failed the blood test and calling it a day?
I watched this last night and that really stood out to me. They kept acting like everyone was doomed and there was no way they were going to escape this situation, but it seemed to me like they were on the right track.
Just give everyone the blood test, and if someone fails, burn them. Once they've gotten everybody, the Thing is dead.
Right?
". . . burning everyone who failed the blood test and calling it a day?"
Your apparent confusion is confusing. This is exactly what MacReady had in mind and exactly the plan he was implementing. Ultimately it failed because Blair had escaped the shack he was locked in.
As for the bewilderment surrounding each little piece of "the thing" being alive in some sense...first, this is a point where you should accept that this is a movie involving an unstudied creature from outer space. Anything goes so long as it doesn't fly in the face of science as we know it. Second, a scientific explanation could be that even if an individual cell is alive, i.e. capable of perceiving its surroundings and sustaining itself long enough to replicate more and more cells, it would probably need a threshold mass of external, living matter to reproduce and divide before it could become a dog, a human being, etc. For cinematic purposes, I think Carpenter and Lancaster put in just the right amount of reasonably plausible scientific mumbo jumbo.