One of the most important things you learn in any job is what's actually safe and what isn't. This is true if you're fueling trucks, raising a kid, or designing spacecraft: you develop a profound intuition for which corners are completely fine to cut and which things you never even slightly mess around with. Most often, as you learn a trade, you more and more realize that things you thought were dangerous are actually safe -- which makes sense, since it's better for those who don't know to assume danger. You end up dividing things into three groups: things that really are dangerous, things that are dangerous unless you know what you're doing, and things which aren't dangerous at all.
Of course, what you really don't want is for a bunch of amateurs to then tell you how to do your job. There's the old joke about how first-time parents, when their baby drops a pacifier, will resterilize it in boiling water; second-time parents will give it a quick rinse; third-time parents will shrug, wipe it off on their shirt, and stick it back in the kid. You really wouldn't want a bunch of first-time parents (or non-parents) passing a law mandating that you sterilize everything. What you want is for less-experienced people to learn from more-experienced people.
In this context, here's an interesting new Pew survey of attitudes towards science. What I found most interesting about it is that a lot of the questions on which there were big differences between scientists' opinions and those of the general public were precisely "is this safe" questions tied to the things that scientists deal with every day.
Most of the time, people who know the subject say that something which sounds dangerous is actually perfectly safe: eating genetically modified foods, eating foods grown with pesticides, getting vaccines, building nuclear power plants (!). Perhaps more interestingly, there are some things which the general public thinks is safe which experts say OH HELL NO GET AWAY FROM THAT SWITCH YOU LUNATIC to: allowing climate change and increasing offshore drilling being the two most notable examples. That's part of the same kind of professional eyeball: sometimes you know that something is just a giant deathtrap waiting to happen. Turns out that offshore drilling rigs are far, far more alarming to professionals than nuclear power plants: the former fail all the time, in horribly disastrous ways, while the latter are actually pretty reliable, all told.
We can talk about lots of reasons for this: for example, the media loves to make things sound really scary (because that sells newspapers), or people don't know enough about the details. But really, what's going on is simply the judgment of experience: people who work with various strange and foreign things, day-in and day-out, tend to get a pretty good feeling for what does and doesn't matter. And it's not always going to be obvious which is which: you just have to ask people who know.