see, in the movies, time travel was possible, but it was hard. it could only be done from the future going backwards, and once you went back in time you were stuck there. in the series, they did it fairly easily. if they can time travel so easy, why dont they go back and stop everyone from making SKYNET in the first place, and avoid all the drama and killing? i mean, they could just turn the guy who made TURK on to heroin or something. or since he had a thing for Sarah Conner, she could be his girlfriend and she could sabotage his work all the time without him noticing.