The case for smart contracts is, you can't have disputes. No need for attorneys, that will bleed you dry. It does not add an additional layer, instead it removes them all and becomes the sole layer.
Now what? How can't we have disputes, we did a "smart contract"?
That means I can’t spend the $100k directly for six months. But, I can easily take out a six month loan against it. That way it’s liquid for me and still safe for you. The loan agent is taking on the risk in exchange for the interest.
Further, how do you select the trusted 3rd party--can't you get screwed here if there are "multiple" 3rd party notaries? As far as I can see, you can't get rid of some "central" authority
If the answer is “corrupt third world countries” ask yourself why the demand is driven by affluent Americans trying to sell things, and how effective “but it’ll go down on your permanent record! In a different country!” will be when the local capo’s buddy tells the notary the car was fine when you bought it.
This replaces attorneys by creating attorney-programmers who charge more and have less recourse when someone makes a mistake.