Archer was desperate when he stole that warp core.
What made him an asshole was that he never went back to see how those lllyrians were doing, floundering at impulse, or replace the stolen warp coils when in the many many subsequent episodes that occurred after damage when Captain Archer had made allies and suddenly had ample resources, if not still later when they were resting comfortably back at home.
Actually I'm surprised that the other Enterprise didn't leave the spare parts the Illyrians needed on a nearby moon, next to a time delayed transponder which Archer could have set up 50 years earlier.
Both of them.
Janeway clearly said to Tuvok who thought that he had a bright idea in The Void that the Starfleet Charter does not justify or tolerate piracy by officers sworn to uphold that charter.
(Ransom would disagree.)