Never run away from the Time Police!

The question depends on what time travel conventions are observed:

The Marvel Comics general rule of time travel states that any meddling done by a time traveler splits the timeline off into a different direction. He will return to an unchanged future; his actions will just have repercussions on an alternate dimension. In this instance, you cannot hold his alternate self responsible for anything. Just the guy who mucked up the other dimension.

The Chrono Trigger rule of time travel, however, holds that the future is fluid, and time travelers are immune to any changes they make in the time line. (There's only one exception, Nadia's disappearance in 600 AD as a result of her own time traveling). In this case, you CAN hold Crono and company responsible for the thousands of people who existed in the ruined future, who are now shunted off to the Tesseract along with Lavos!

The convention observed in Prisoner of Azkaban is subtly different again. Here, there is just one timeline. Whatever happened, will happen. All time travelers will just end up making it happen. This creates a dandy time paradox of course, but in this case, you CAN hold the time traveler responsible for their mistakes.

But I haven't fully answered the question, did I?

In Janeway's case, she hasn't committed the crime yet. But she did knowingly change a timeline in which the Federation got hold of anti-Borg weapons. Because of future Janeway's selfish desire to save some of her crew, she sacrificed the acquisition of that knowledge. And may have doomed millions to assimilation. So, yes.

How ya doing, buddy?