the entire argument is that you can not apply laws retroactively.

It's not retroactive! The law was not passed today! It was there from the beginning. It's just that Apple didn't care until today when they were told to pay. So suddenly they don't want to pay what they own because the 'didn't know' so they call this "retroactive" even if it's very much not retroactive at all.

So you're saying, if I rob you today and you don't get around to reporting the crime until next year, I should walk free?

There are actually limits to how far back the dodged taxes can be collected. That's why it's only $13bn. That's what has been due since 2003. This entire thing actually goes back since the 1990s.

Also, we're not even talking about criminal charges or fines here. Apple isn't being sued or facing any punishment. The EC has merely ruled that Apple didn't pay all the taxes it legally owed Ireland and Ireland didn't have the authority to allow them not to pay the taxes in the first place.

This is akin to a janitor charged with collecting rent for the landlord telling you for years that it's okay for you to pay pennies to live in your mansion until the landlord finds out about it and now demands you pay the $$$ you owe him because the janitor was never legally in a position to make that kind of deal and you're actually a highly paid expert in rental contracts and were fully aware of the deal having no legal basis to begin with.

This decision can't have been a surprise to Apple. Seeing this kind of thing coming is what they pay very expensive legal experts for. They knew EU law overruled the Irish laws that supposedly allowed this deal in the first place. They're only crying foul because they were caught.

My reading of the ruling is that the EU are saying that it's always been illegal under EU law, but that the Irish government had pretended that it wasn't.

What it looks like they are trying to do is apply a legally compliant level of taxes retroactively, not laws.

But you can, because the tax breaks we unlawful this whole time! That is the entire point. If I break into a warehouse and steal a TV every day for years can I just argue "ok I'll stop but you can't punish me because you can't apply the law retroactively"?

That's a broken argument since what they are stating is that a higher law was broken. It's also not always the case that laws do not apply retroactively:

https://en.wikipedia.org/wiki/Ex_post_facto_law

We should apply this to murder as well.

(Yeah, I know you're saying it was legal under Irish law, but the whole point is that some Irish laws take precedence over others. In this case, their treaty obligations to the EU, codified in their laws, take precedence. If this wasn't the case there wouldn't even be a court case, much less a judgement.)

> the entire argument is that you can not apply laws retroactively.

That only applies to new laws.

which is not the case here.