>contaminating a place where we might someday search for life
Should it have crashed into a moon that we later find life on (especially should the life be remarkably similar to that here on earth), whose to say we didn't send it there via Cassini in the first place? Avoiding this problem entirely seems to be the best bet, also allowing them to collect atmospheric data from Saturn on the way out.
In some cases we could still estimate a probable answer.
Biologists can separate two cryptic species of living beings placed into an species complex, just taking a look to its DNA. The mutation rate among two isolated bacteria from earth and saturn would be noticeable. Unless we discover an active saturnian's nano-turism to pass the holidays on earth's oceans, the only reasonable answer to explain two identical or almost identical bacteria in both planets is a contamination event.
Should it have crashed into a moon that we later find life on (especially should the life be remarkably similar to that here on earth), whose to say we didn't send it there via Cassini in the first place? Avoiding this problem entirely seems to be the best bet, also allowing them to collect atmospheric data from Saturn on the way out.