In the episode "Demon""Demon", the crew of Voyager give their DNA to not only a pre-warp civilisation but a pre-sentient civilisation, changing the course of their natural evolution. This seems to me to be a clear violation of the Prime Directive which states that ship's captains should avoid interfering in the natural evolution of less advanced species.
So why did Captain Janeway feel that she could violate the Prime Directive?