I think technology used in sport would be useful, to stop some poor decisions. But in that match the points should not have been given to spurs because it is possible that if that goal went in it would change the entire way both sides played for the rest of the match, and there is no guarantee of the scoreline, so it would be stupid to do so.
And all the times that other obvious goals were disallowed, i don't think it would be right that only in this case the result would be changed.
I would argue that most of it is because the goal was against man u, and most people have a dislike to them so want to see it changed. When decisions of clear goals go against man u (i'm thinking for example paul scholes goal in the champions league which was clearly on side, but was disallowed), there is nowhere near this level of reaction, even though the game was alot more important.