People get riled up because of an exclusively American twist to their corporate tax rule which allows American companies to defer paying US corporate tax on foreign earnings until the money is "repatriated". This is why you never see UK, German, Japanese, etc. companies use Ireland as a tax "haven".
Ireland follows international law in taxing multinationals on the profits generated in Ireland. When you hear a claim along the lines of "Apple only pays 2% on its revenues in Ireland", it's because the vast majority of the profit is taxable in the US not in Ireland but payment is deferred because of this US tax loophole. Just because the cash hasn't been handed over to Uncle Sam, doesn't mean it isn't due.
It's perfectly understandable that the US government is unhappy at this attempt by a foreign government to grab corporate tax which by all international standards belongs to the US treasury. If the EU (and I'm a proud European) wants a share of digital tax, then they should grow their own profitable tech companies to tax instead of selectively eyeing up US tech companies. The US doesn't get to impose corporate tax on German car makers or French wine producers - nor should the EU get to impose a corporate tax on US tech companies.