Tax evasion is simple: people not paying the taxes they are owed to the government. What you are referring to is tax avoidance or minimization, which is fine (or rather, another problem, mostly the governments)
"When people talk about companies evading taxes, they're really working through the tax code."
Switzerland facilitates tons of actual tax evasion, which they are not supposed to do, and which is illegal in the US.
From [1] "the Swiss financial sector and the DoJ began a decade ago when whistleblower Bradley Birkenfeld provided evidence that his former employer, UBS, was helping wealthy Americans evade taxes.
Switzerland’s largest bank was fined $780 million in 2009, but it was later discovered that other Swiss banks had been poaching UBS clients after the criminal probe had been announced. "
Switzerland is party to many treaties with EU, US etc. - and they (gov. and banks) know exactly that they cannot facilitate tax evasion, if so, it becomes a crime.
This is not ambiguous.
If you, living in Switzerland, help facilitate a crime such as murder (i.e. totally unambiguous) in the US, then the US will extradite you even though you may not have broken any Swiss laws.
Tax evasion is a crime like any other, hence extradition and arrests etc..
Though some cases may have some ambiguity i.e. (what constitutes 'aid' and maybe some hairline differences between 'evasion' and 'avoidance') - in general, it's crystal clear: if you help people with tax evasion, you've committed a crime.
And FYI - the reciprocal works just the same - if you murder someone in Switzerland, but have not broken and US laws, you can be sure that the Americans will arrest you and send you to Switzerland if that's what the Swiss authorities want.
[1] https://www.swissinfo.ch/eng/-5-million-fine_swiss-bank-sett...