The reason behind "permanent" banning?

[TryNinja]

I will quote the original post of theymos later, when I saw it again, not found ATM.  I don't remember where I read it

He also makes that clear here:

Anything that'd get you expelled from a university for plagiarism (which all of the above-banned examples would) will get you permabanned from this forum, regardless of your rank.

[logfiles]

Recently, I read the following thread:

https://bitcointalk.org/index.php?topic=5104259.0

...and felt bad for its OP. It looks a bit harsh and cruel to permanently ban an account for spamming, plagiarism, or whatever the (similar) reason is.

It feels a little harsh but rules are rules, my friend. Every community/society has a set of rules where the acts of against them can't be broken. Once you try to bend the rules because of one user. Then you will start raising questions and destroying the communities moral code.i
In Bitcointalk plagiarism and other acts of spamming are considered bloody evil and every user must know that it can get you banished for life.

[YOSHIE]

I understand what you want, but keep in mind that everyone here is a bitcointalk member, "nothing more," a privately owned forum.
"Who is the one who punishes and who makes the rules in your house, the answer must be you ...? There's no way other people will take over.
This is not a government that has combat troops, judges and police who punish those who are wrong in prison or fine.
The rules forum already exists, just living it, if you can't afford to leave it, make it easy?
You know the English royal system, which was wrongly removed from the palace or the death penalty. Depending on the level of error.

[Hivalley]

You should also understand and take note that not all offense leads to a permanent ban,there are other punishments that are applicable based on the offense committed
Some attracts a temporary ban for a specific amount of days,while some accounts are nuked
While offenses such as plagiarism attracts a permanent ban,and I think it's a well deserved punishment and should not be reversed.