Yeah but even if you videoed every tackle and replayed it to the ref you're still going to get disputed decisions because in many cases it will always be down to interpretation, just see how many times the pundits disagree over a tackle or a penalty.
Football is at its best as a game that flows, constant stop/starting could potentially ruin it. As for cards/penalties ruining a game, well yeah sometimes they do, and sometimes they're the reverse. As my dad always said "sometimes 10 men fight harder than 11" and it's true, similarly an unjustified penalty can galvanise a team, how often have you seen games where one team don't actually start playing until they're a goal down.
I'm not against technology, I think goal line tech is long overdue, but I don't want it to go beyond that.