First, let me say, I am posting this in the spirit of a friendly discussion, and if I make extreme remarks, it is to emphasise a point rather than to cause offence. Mind you, facts are facts regardless of whom they offend.
1. Death Penalty is Uncivilised.
There are so many reasons why the death penalty should be regarded as uncivilised. Roughly two out of every three countries in the world agree that the death penalty should be abolished worldwide. These countries include most of the European ones (including Austria, of course), Canada and Mexico, Australia, and NZ - all of which can creditably be regarded as among the most civilised nations in the world, and whose criminal justice systems have delevoped to a reasonably high level of sophistication.
Countries which haven't include among their number, Afghanistan, China, Yemen, North Korea and Zimbabwe. Many of these countries can claim to be civilised - Japan, for example - and to have developed legal systems. Most, however, are not the kind of place you'd want to get caught in for committing any crime ... Saudi Arabia or the Yemen, for example. So the balance in favour of "civilisation" tips heavily in favour of the abolitionists.
It is also interesting to note that, of the retentionist countires, just six of them account for more than 90% of the executions, with China being way out in front of them all, but with USA featuring in the list of 6 most bloodthirsty nations. A proud boast for a civilised nation! Especially when you look at which the other ones are.
Even USA'a quasi-colony in Africa - Liberia - has abolished it.
Other reasons why it's uncivilised? It's random. If you're convicted of a capital crime, you may or may not be executed. It costs more (this is surprising at first, but it's cheaper to imprison a person for life than to go through all the legal processes necessary to confirm and carry out an execution - when you consider legal costs in the highest appellate courts, you'll begin to understand). Poor criminals cannot afford good lawyers, which in an adversarial legal system is more important then proof of innocence. It's irreversible. About 10% of people sentenced to death in USA have been found innocent before sentence was carried out. Good for the appeal system (partyly why it's expensive) - but if that many had the good fortune to discover new evidence to prove their innocence, then how many innocent people were unlucky?
OK, there are many more reasons why the death penalty is regarded as uncivilised, but I think I've made my point. I'm sure many readers here will disagree, and I don't want to read reams and reams of rebutals.
2. Mad people cannot plan ahead.
Nonsense!
3. The test for insanity is not knowing what you are doing.
Seung-Hui Cho? Maybe you think he was sane.
Trying to conceal your actions, even if you know they are wrong, is not proof of sanity. Otherwise every disgraced politician is insane (Nixon, Carter?). Maybe I'll get no argument about that!
Fritzl says he knew what he did was wrong, but he couldn't help himself. A plea of insanity. I'm sure the Austrian courts will have appropriate tests that are a little bit more reliable than "Wußte er, was er tat?"
4. The World wouldn't have given a Toss if Hitler had confined his Final Solution to Liquidating the Insane.
I think there are many who would disagree.
5. Fit punishment.
Broadly, I agree, although I would point out that Fritzl was already a convicted sex offender, so he is a danger to all women still. He must be removed from society - in my opinion, forever.