While I agree that we should spend more on infrastructure, that too is a political argument (deciding what's "an important purpose").

Krugman has every right to express his political views, but it should be clear that he's doing so.

We know to a high degree of confidence that investments in infrastructure give a good return on investment. The trickle-down theory has remarkably little evidence to support it. It's a perfectly reasonable economic argument that deficit spending on infrastructure is sensible, while running a deficit to fund tax cuts is a bad idea.

> We know to a high degree of confidence that investments in infrastructure give a good return on investment.

No, we know that some investments in infrastructure give a good return on investment. Some don't (bridge to nowhere, for example). The problem is that Congress can take useless make-work pork-barrel trash, and label it "investment in infrastructure". Don't automatically believe the labels that Congress applies to bills; they often are political smoke screens.

Note well: There is real infrastructure investment that is needed, and will give a good return. All the more reason to reject the waste - we need the money for real things; don't waste it on pork.

Every time a factory moves to a new location with lower taxes, or a wealthy person transfers assets to a tax haven, or a company refuses to repatriate earnings because of taxes, we see evidence that lower taxes have economic benefits.

Locally and short term that is the case, but looking at the bigger picture a race to the bottom can lead to worse outcomes overall.

Not saying that is definitely the case at any particular tax level, but it's not as easy as looking at the individual cases.

I honestly have never seen that evidence. I've heard it used as an excuse the last 40 years to lower high income taxes though.

Any sources/links/examples?

You haven't heard about the hundreds of billions of dollars companies like Apple and IBM are holding overseas, or the number of companies that have invested in operations in (for example) Ireland?

https://www.theguardian.com/world/2015/mar/05/ireland-attrac...

> A major draw for US firms is Ireland’s low 12.5% corporation tax rate and numerous controversial tax breaks. The government has promised to phase out the latter.

> The corporate tax rate, which remains a sacrosanct part of Irish industrial policy, has been so successful in wooing US investment that the country’s neighbours across the border want it too. The Northern Ireland assembly passed legislation this week allowing for corporation tax powers to be devolved, with politicians at Stormont aiming for a similar rate.

Oh, I have.

I have however not seen any proof that it benefits the country other than employment (how are the salaries?).

If you look at tax revenue as percent of GDP it's almost had a freefall [1], which could be okay if the GDP is high enough.

In direct numbers however Ireland as of 2014 was not even back to 2007 levels in tax revenue (pre economic crisis) [2], and ignoring inflation. And only counting corporation tax, not even back to 2002 levels.

[1] http://data.worldbank.org/indicator/GC.TAX.TOTL.GD.ZS?locati...

[2] https://en.wikipedia.org/wiki/Corporation_tax_in_the_Republi...

We should separate the arguments "lower taxes benefit the economy" from "lower taxes increase tax revenue".

Both of your observations address the latter, while I made the former.

You're right, they're two different arguments. But I don't think it's a far leap looking between different countries to say that good infrastructure, healthcare, welfare and through sensible regulations an empowered workforce is also good for the economy.

Looking straight at GDP (even if it's a blunt instrument), Ireland hasn't reaped a lot of rewards there either [1].

[1] http://www.tradingeconomics.com/ireland/gdp

Ireland was hit hard by the financial crisis; change the time scale on the graph to MAX to see the rewards Ireland reaped before that.

And their growth over the past few years appears to be back to pre-crisis speed.

They started lowering the corporate tax in 1995, so if you look at the graph from 1995 to now and compare it to the US graph from 1995 to now, the curves are nearly identical, only the US is much less fluctuating.

If by nearly identical, you mean growing twice as quickly.

That page allows displaying both on the same graph (compare to "US GDP") and when placed by side by side it's easy to see that Ireland has grown at least twice as quickly since 1995.