At least, that's how it was regarded in traditional societies. A Traitor being someone who poses as a friend, but works for the enemy. Far more dangerous, more damaging, than a known enemy...
From a 'natural justice' perspectives it seems unsurprising that it was the last remaining crime to be punishable by execution; and also that to the modern secular Leftist way of 'thinking' treachery isn't a bad thing at all...
It was the upper class communists in Europe, the UK and the USA who made treachery into an 'acceptable' option; by working for the Soviet Union and against their 'host' nations (as parasites, they saw their own people that way).
Nowadays, it has become infra dig, a mark of low-class loser status among the Establishment, even to think about the possibility of treachery. Again, no surprises; considering the entirety of the ruling Establishment are themselves traitors; blood-sucking leeches growing fat from devouring the resources of those whom they purport to lead and guard.
That this is the case in politics is obvious, yet still not fully appreciated - at least in Britain. That the Left have been solid traitors since the middle 1960s, loathing and despising those whom they claim to 'represent', is still denied.
But it applies across the board. Someone who is a traitor and nothing but a traitor, such as Theresa May, is instead the object of sympathy or regarded as a well-meaning incompetent. Something like the Conservative Party is institutionalised treachery; yet people still regard them as superior to the leftists; when the difference is merely between species of Quisling.
The people who represented the medical profession in the 1900s were all traitors; and that the same applies to those who are the leaders of science: the 'great and good' of the peer review cartels. Yet this simple, obvious fact still is not acknowledged.
The leaders of all the mainstream churches are not benign bumbling fools - they are traitors, plotting and scheming how personally to profit from their employment as destroyers of their churches, while rehearsing conciliatory hand-wringing and concerned frowns...
It could not be much more obvious - yet most people don't see (and congratulate themselves on their blindness; as if being a smirking dupe was something to be proud of...).
The mental convolutions through which people will spin in trying to deny common sense and the evidence of experience is remarkable.
Sometimes - indeed, usually - things are as simple as they seem to be. The reason They fail - again, and again, and again - is simply because they are not even trying to succeed.
This basic fact needs to be clear before we can proceed - which is exactly why so much effort is put into obfuscating it.