There are those who say we should not be responsible for seeing to it that the least-earners among us have health care, sick days, etc. But that whole petri dish thing... that's the result.
Joe the McDonald's window guy has flu/whatever, but he can't take a day (or 3 days) off (might not be allowed to, but can't afford to anyway so, the former is moot.) So Larry goes for lunch, and comes away with whatever Joe had as a bonus. And that goes on all day, for several days. While everyone else in the McDonald's catches it too, thereby extending the event even further, basically until every employee's immune system have handled the problem. And of course, there will be the occasional person who can't manage it -- for whatever reason... compromised immune system, preexisting disease process that complicates matters, old age, whatever. For them, matters can be much worse.
Either we admit that we need to take care of everyone, for everyone's sake, or we'll just keep running into situations where transmissible diseases have far more chance to spread than would otherwise be the case.
Odds are excellent that the only thing unique about the Disney event is that someone noticed it. Most people have probably been on the receiving end of such "petri dish events" many times. Anywhere you have a person with a transmissible disease in a condition suitable for transmission (usually not the entire course) that faces the public, the potential exists.
Anyone in that state should be in bed, properly isolated and medicated. Every time that doesn't happen, we're just shooting ourselves in the foot.