Re: Is it so easy?
Well that is the issue. It is not so easy to create a law - which has to be black and white once case law is created. Any grey areas just create loopholes and tax avoidance.
So, if you say that a lot more 'product' and 'sales' work goes on in the other countries - then is this the definition in law? Every country that has more customers than the parent company has to be set up for local taxes on all customers in that country?
Not exactly fair though is it. If, the UK for instance, has 1million customers of company x and they are based in Ireland which has 900,000 customers then they pay corporation tax to the UK? However they have a push and get 1.01 million customers in Ireland and now they can stop paying tax altogether in the UK? What about smaller countries with a lower user base, will they never get tax from any business that isn't based in their boundaries?
Maybe it goes on company size? Well Google employ 3000 people in Ireland but only 1,300 in the UK. Therefore they would be right to HQ in Ireland, surely?
Maybe everywhere you have a customer you have to pay tax on that customer? Well this isn't corporation tax, it's duty and VAT.
So do you split their profits among all the countries based on a factor - but what? Customer size, Customer revenue, staff numbers? This would be a loophole any decent accountant could drive a truck through. You are likely to kill off the super-widget maker's dreams of European sales mentioned above. What if the customer buys goods from the internet in a country that doesn't actively market there?
In reality in a free market in Europe a company should be allowed to choose when to set up their headquarters. The same way that Wales or Scotland might reduce taxes for the Amazon warehouse in Swansea or Edinburgh. The same way you can choose to buy something from France if it is cheaper and you live in the UK.
It's not straight forward, if it was then there'd be legislation already.