Can we leave politics out of this, please?

Look at it from an individual business' point of view. International trade has challenges. You have to deal with different rules and regulations, custom checks, tariffs and who knows what else. I would know: unlike you, I grew up in a country where our company had to deal with such things on a daily basis.

So any individual business has to make tough choices: do we trade internationally or not? Is the extra hassle and associated costs (staffing, training, keeping up with regulations in all our export markets...) worth it? Or do we go the easier path and trade just within our own country and forfeit a bigger market?

This is where the idea of a single market comes in. It expands what "within our country" means. It makes it easy to forget that Finland, France, Germany, Slovakia, Romania are different countries. From an individual business' point of view, it makes no difference whether you are buying from or selling to Helsinki, Frankfurt or Milano. That, my friend, is the exact opposite of "not allowing free trade".

The drawback is that it may have worked too well and made things too easy. So easy that some businesses (such as Jolla) are content with the market of 450 million and do not bother with all the hassle of looking beyond. Especially considering that those 450 million cover most of the richer part of the world. (BTW, we see the same in the US, where many US companies do not know how to trade outside the US and where most people do not even know the international dial prefix.)

What is worse, the single market made trading so easy that some people, particularly in the country that has been subject to decades of relentless anti-EU propaganda, forgot that it was the single market that made it easy. They take their luck and privilege for granted and are whinging when they foolishly throw it away and suddenly see the consequences. Like, for example, Brexit voting British fishermen.