I didnt think the show was terrible, but I agree with most of the complaints. What I dont understand is if it cost $4 mil an episode, why do they waste that money on episodes that dont advance the story? They could have told a complete story in 13 episodes, but instead they dick around with a family drama, that wasn't even good by family drama standards. If you take all the elements that advanced the story from all the episodes, they probably only add up to one or two episodes. Its too bad this kept going for as long as it did, but a show like Lone Star gets axed after 2 episodes. I'll never understand Fox.
I think they said something about disturbing the ecosystem and the past to much, which would effect the future. But hey, it's not like having humans go back in time didn't mess with that already.
I believe they thought they were on a parallel earth, so it wouldnt effect their present time.
A better version of this type of show is called Outcasts, which ran on BBC.