Nobody demands that everyone should be happy about Brexit. It’s in the nature of any major decision – and particularly one decided by referendum after more than 40 years of trying to avoid the issue – that there are some who deeply dislike it. That’s fair enough.

But it’s not unreasonable to ask if some of the wilder hyperbole about Brexit is really sensible or true. Some of what is said about the “destruction” of the UK, economic apocalypse, and even total isolation of the country is plainly absurd. Surely such obsessive pessimism merits challenge, for the good of sensible debate as much as the good of the nation?

Whenever anyone does raise this question, however, the response is predictable: The Brexiteers can’t accept dissent! They think if only we become fantasising optimists like them then the problems will go away! Clasp the flag in each hand and sing Rule Britannia as the ship sinks in the hope of divine intervention!

That response comes from the same source as the wilder hyperbole about the harm done by Brexit: a belief that the issue is not a division along the lines of analysis and belief but of sanity, reason and honesty. If you think all Leavers are either mad liars or mad people who have been lied to, then it follows that anything they say must be mad, a lie, or both. That’s wrong, of course, but it is at least consistent.

The original point – that we need to challenge the tendency among some to always believe the absolute worst about leaving the EU – still stands, however. That’s what the Prime Minister is reasonably doing at the CBI conference today with her appeal to “rational optimism”.

Note the word “rational”. This is no appeal to blind belief or denial of any fair concerns, but a simple call for a reasoned assessment of the opportunities that lie ahead of us. If you still deeply dislike Brexit, that is your right – but as it is happening anyway, the sensible and productive thing to do would be to seek out how to make the best of it.

What the Prime Minister didn’t say, but could have, is that there’s a far greater cause for concern on the horizon for British businesses, anyway. His name is Jeremy Corbyn.