There are signs to not go swimming. There's a difference. And I agree, it won't stop everyone. But it would the majority. And, I also agree it was an accident - however, it was an accident that may have been able to be prevented, and we all know that legally, if they decide to sue, Disney is going to be liable, because they didn't have proper precautions in place.
As far as one of the other comments that Disney has been doing a great job since this is the first incident. Yes and no. A) You have to look at increasing population. The gator population was much lower in the past years of the park and the risk was much lower. The population has really exploded over the last decade. B) Disney's population has also been exploding. More people = more risk. Also, more people = more feeding = more alligators. C) The fact that anything hasn't happened previously, aside from the fact that there was reduced risk, is largely just luck. They've been capturing/trapping them yes, which is very important, and I think they've done a good job, but as others have mentioned - they'll never capture them all, as evidenced by the fact that people see them in the park and resorts. And because of that, they need to be doing public education/awareness - which they haven't been.