Re: Endgame and the Unicomplex (spoilers)
I hate Temporal mecahnics.
But what should have happend is in the future starfleet would have monitored Janeway's escapdes and sent back people to undo her changes. After all VOY introduced the concept that in the future the Federation monitors the timeline so "Endgame" should never have happened and VOY should still be on her way home.
I hate them too.
I always found the idea of Starfleet "time cops" to be rather silly myself, and I think real time travel - assuming it's possible - would require a lot more variables than the rather simplistic version we usually see. I think this was done well with the Krenim time ship in "Year of Hell," where Chakotay tried out some simulations and realized he could easily screw up a whole region by not factoring in the history of one element.
"If you think you're brave enough to walk the path of honor, then follow me into the dragon's den."