Touch scares are a tricky one. For some people, there's a huge fear of what could happen: a lot of people worry about being touched and having their personal space invaded. But once that wall is broken, some can lose that fear (because you realise being touched isn't that bad).
There's then the other side that when touching is allowed, actors can become over-reliant on it. Even for people who don't like it, you can quickly become desensitised to it, and ultimately it loses its value.
Plus, touching doesn't always ramp up scars factor. Sometimes it can take away from the experience, take you out of the story ("why is this butcher who wants to take me away, kill me and sell my meat only stroking my head?" For example). It has to have a reason and be timed rightly.
Personally, I reckon touching works best when it's a bit more full-on (say, Sub Species style, where you can be forced to go in certain ways, etc). Anything less than that rarely increases scare factor imo