You cannot depend on warning signs to keep people out of trouble - they can be too easily ignored or the importance misunderstood. Sometimes adults, even with known (minor) health problems, will get on a ride "for their children" when they otherwise shouldn't. Even rides as tame as Kilimanjaro Safaris and Spaceship Earth have some type of warning now, for little apparent reason (ride may be jarring and vehicle rotates, respectively). So, if the "warning" on such a tame attraction turns out to be nothing, can't a guest then reasonably assume the Mission Space warning is all hype and can also be disregarded?
While you certainly need to warn someone with a heart condition before boarding Space Mountain, for instance, probably most people - even with such a (presumably minor) condition - who are healthy enough to walk around the parks all day would not usually be harmed by a trip on the coaster. That certainly does not mean they should ride, because it would be dangerous to some of these individuals - hence the warning - just that most people likely would be fine even if they (foolishly) ignored the warnings. No doubt this happens everyday.
But something different appears to be happening on Mission Space. People in good health - without any condition which should exclude their participation - are sometimes getting sick. Obviously, the warning signs for this attraction must be taken seriously - but are they? Since this is a Disney attraction, it can't be that extreme, right? They have to have those "legal" warnings and all, but since its in Epcot its really safe for everyone from toddlers to great-grandmothers - right?
Not in this case. Which brings up a very important question: Even if the attraction were found safe for persons in better than average health, out of consideration to the numbers of children and seniors (and us chickens who also won't ride the thing) which tour the WDW parks daily, should you really feature an attraction which is potentially harmful - and therefore off limits - to such a large segment of your guests?