There simply is no good reason short of war or sanctions not to buy it from the cheapest source.
Sure there is. National security. If Russia are the de facto enemy (they are, that's why NATO still exists), then energy dependance on them to save a few euros is stupid.

And it's not Trump's place to publicly scold other countries on how they do trade
It isn't? But it is every other leader's place to meddle in American politics by critisising Trump? Trump's job is to do what's best for USA, and if he thinks scolding other countries is one method of going about that job, then good for him. I'm glad he's putting pressure on May. We voted OUT, and the bitch is not delivering. Someone needs to meddle, because democracy isn't working.

Since it's not, it's up to those countries to decide where to buy their fucking gas.
Yep. But if Germany wish to say "hey, Russia aren't so bad, we're buying gas off them and they're not squeezing our balls", then why the fuck don't they leave that anti-Russia defence alliance they are a part of?

My problem isn't with Germany buying gas off Russia, my problem is NATO and the fact we're paying ridiculous amounts of money to prop up a redundant defence pact. The fact Germany are energy dependant on Russia exposes NATO for the crock of shit it is.

That's not the "point" of NATO. The whole idea behind NATO is its members share certain ideological principles such as democracy and freedom from tyranny, and are only committed to support each other in defensive wars.
You should be a politician. You have an amazing ability to turn an anti-Russian defence alliance into a beacon for democracy and freedom.

It's point is not to try to ruin countries that aren't its members, or refuse trade with them
Are you pretending to not know how NATO came to be? It was formed to counter the growing threat of the Soviet Union. It's very existence owes itself to the beginning of the Cold War.

The point of NATO is simple... it is a defence alliance. There's no "common principles", otherwise what the fuck are Turkey doing in NATO? The common principle is fear of Russia.

So it's not about refusing to trade with non-member states. It's about refusing to be energy dependant on the very nation you de facto declare as the enemy by virtue of membership of NATO.

It's basically just a nice insurance policy.
Insurance against Russian aggression.

Who is NATO creating problems for? Russia does not fit into the mold of a democracy, unfortunately. You might as well argue NATO should be replaced with a bloc that includes N. Korea, Iran, and China.
It should be open to anyone who wants to be friends when it comes to military. Economics and politics should have fuck all to do with it.

Turkey are a member state. Turkey. Did you see that recent purge? They're as democratic as the contents of my arse.

Haha, the Russian influence on Trump is much stronger than their influence on NATO.
Oh yeah I forgot he's having a homosexual affair with Putin.