Nobody's saying people shouldn't also read the prospectus. But if people can lie in the pitch and then get out of responsibility through an obscure note in the prospectus, more people will lie. It allows classic "the large print giveth and the small print taketh away" scams.
Civil litigation is a terrible method for enforcement. The longer the feedback loop, the more opportunity for things to go wrong. Short-sightedness is a defining characteristic of most scammers. And litigation will only happen when there's enough money at stake and the chances of recovery are high. Small investors are fucked from the start, as is anybody who gets taken by somebody who spends the money in ways where there's little to recover.
Also, your "bad actors" vs "good actors" thing is a total false dichotomy. Actors aren't the problem; it's actions. If you make it easier for "bad actors" to act, you will have more (and more severe) bad actions. Further, through competitive effects, you push everybody in the direction of bad actions.