Let's tally up the "Time Crimes" the Avengers were allowed to get away with;
Hawkeye removing an object from an existing timeline and not returning it (the baseball glove), War Machine knocking Quill out long enough to steal the Power Stone (that's possible brain damage altering any future decisions he's supposed to make), Thor inadvertently warning Frigga about her own death (she is an extremely perceptive being, who would have known what made Thor so distraught upon seeing her), Iron Man and Captain America removing Pym Particles from the past, Evil Nebula giving Pym Particles and a Time Compass to Thanos allowing him to travel in to the future (skipping over events he was supposed to carry out [sacking Zandar for the Power Stone, wiping out half of the surviving Asgardians, etc])
Those are just off the top of my head, and will have caused far more damage to the timeline than Loki not using the Tesseract to escape.
Except everything there was supposed to happen for the sacred timeline. Well, except Loki escaping. That was the only thing they didnt want to happen.