There is no "thin end of the wedge" or "slippery slope" or whatever nonsense idiom one can think up. It's not logical, it's scaremongering. I'm not sure what exactly opponents of "technology" are afraid of. I think they just don't know HOW the technology works, so they assume nobody else does either.
All the time wasted by coaches and players arguing with a referee after a penalty decision is far more time than it would ever take to see the video. Don't have to make a whole ceremony about it, ref should be able to watch it if he wants to. Why in God's name is are you so worried about "time" anyway Biggus? It's wasted constantly in this game, so it might as well be to an end rather than for nothing at all. This "free-flowing" game you speak of doesn't really exist, and as such it wouldn't really be hindered by something that actually made decisions easier.