How are justified the laws about execution abandoned and self-defence allowed?

Question

Some political figures assume the execution of criminals is not allowed, in the name of humanity for moral reasons and things like that. I'm not asking why they think so, nor want to judge them here if it is right or wrong, but surprising to me is that some of them, at the same time that condemn execution of murderers, easily accept self-defense, when it can easily yield into an intentional killing, even probably out of mistake.

For example, compare the two situations:

1. killing strangers who enter your home will be allowed at least if you know/think they have guns with them. But maybe they are trying to frighten you with a toy gun, or maybe they simply want to take their glasses out from their pockets and you think they have hidden their guns in their pockets, or maybe they are thefts and want to rob something perhaps not even very precious. You should decide in a very short time, and the one has no real opportunity to defend his intention, or explain the situation. Is, e.g., a theft which is never trying to kill anyone be sentenced to death in the blink of an eye? Let assume he is really a murderer, and wants to kill you, then can you kill him and ignore his human right to live his life, even before he does the crime to you so that we can call it a revenge?

2. Someone has murdered several innocents, say children, while was not drunk, out of intention, and all these are well documented and proven, and he has even confessed about it. People might think anyway his right to live as a human still persist, because e.g. we do not know what conditions in his life has made him reach to this poin to easily kill the others, and that maybe all the society is a share in him becoming such, and so many other justification. So he should be given the opportunity to continue his life but either in a hospital to receive drug or in a prison for the others to be safe from him, and may be even gets free some day if a judge identified him ready to return to the society.

Apparently, at least some political figures (maybe some democrats in US, though not sure) allow self-defense yielding into death in the first situation, at the same time that they condemn the death penalty in the second situation. Isn't it a contradiction with regard to human rights and morality? In the former case the person is not considered to deserve the opportunity to live his life although has not yet commit a murdering (and maybe had never intended such either), while in the latter case the one his life is considered sacred such that no one in no condition should be allowed to take the life of someone God has gifted to him, or simply because human right for living is acceptable by any common sense.

Answer 1

So, the new Q seems be to how do some/Democrats believe in stand-your-ground laws but reject the death penalty.

I'm not denying there might be some in that box, but I'm skeptical this a politically very meaningful Q, because the percentage of Democrats who reject the death penalty is about the same as (or slightly smaller than) the percentage of Democrats who (also) reject stand-your-ground laws.

As of March 2015, 77% of Republicans, 57% of Independents, and 40% of Democrats said they favored the death penalty. 17% of Republicans, 37% of Independents, and 56% of Democrats said they opposed capital punishment.

And

A [2013] Quinnipiac University poll [...] shows 75 percent of Republicans support "Stand Your Ground" and 62 percent of Democrats are vehemently opposed to the law that gives individuals the right to use deadly force to defend themselves without the obligation to retreat.

Yeah, without an actual individual correlation I may be committing an ecological fallacy here, but the Q doesn't look incredibly compelling, in terms of numbers: (slightly) more Democrats seemed to oppose the average person killing some intruder in their house than the state applying the death penalty. (At least in 2013-2015, for when I found those polls. Perhaps there are newer ones, but these were the first ones in Google for me.) Considering the typical margin of error of such polls, the numbers are barely distinguishable at 6pp difference.

FWTW, a Harris campaign spokesperson later said Harris was joking about shooting anyone who intrudes her house. So, right now IDK who'd be the prototypical politician that supports stand-your-ground laws but opposes the death penalty.

Answer 2

The post was closed for several days, within which period the question received some reactions in the comment area, which I might be able to conclude it by the comments by @Lag:

It is only "contradictory" if one believes that one must never act so as to end a life regardless of any circumstances or any consequences.

and

Further to David H's comment:

(1) We don't expect a householder, in such rare and frightening circumstances, to have the capacity, capability, firearms knowledge or mind-reading ability to establish an intruder's intent or if a gun is real.

(2) Generally, householders don't want to kill people, they want to stop the threat - to incapacitate an intruder or cause him to leave. Unfortunately, death is a risk of use of force.

(3) Self-defence != revenge.

(4) One can oppose violence generally and also believe it's justifiable in specific circumstances (such as self-defence or arrest).

My own understanding is that the human right for living is conditional even in West (we do believe so as well in Iran/Islam), if another guy is afraid of his own life, or even his own goods, he is allowed to kill you to make sure you have no threat against him (this is not acceptable in Islam). Apparently this is obvious to those who live in West, so that they see no contradiction here to need resolution at all, and all the evidences that I proposed to support the contradiction idea here seems reasonable or obvious only to myself, or people with similar backgrounds.