Is it wrong to be sceptical of something you do not understand?
It is wrong if you could make a better effort to understand it, yes.
Do our elected politicians understand what it means?
Considering they work with it and have to read these things before they sign them, I'd say they probably do.
If so, why aren't they telling us in words we can understand?
They're not really being asked. A hell of a lot of people just leap on either the anti-EU or the pro-EU bandwagon and from there the only questions that get asked are rhetorical. If you want to know more, speak to your MP, and if they don't know it's their job to ask the gov't in parliament. As they do frequently (though not much over the EU) in Prime Minister's Question Time.
Politicians do have a role in informing the public, but do you know who the bulk of the responsibility lies with? The media. And the best-sellers (such as the esteemed Mail) jump on those same bandwagons because that sells more papers. They might not if people weren't buying them, though...