Executions in Middle earth

[Valandil]

I don't think any of the Middle Earth societies would have been against the use of executions for capital crimes. Elf, Dwarf, Human... whatever.

I don't think Aragorn was ushering into Gondor a more 'enlightened' period with his pardon (from a death sentence anyway) of Beregond.

Aragorn was exercising his right to grant mercy. For more than one reason, I think. Firstly, that it was not a day to pass sentences of death - for a great victory had been one. Secondly - and more importantly - he judged that Beregond had acted rightly, and that Beregond had judged correctly - that it was needful to force his way into the place, whatever the cost might be, in order to save Faramir's life.

I don't think we should extrapolate this any further, as regards future attitudes of Gondor's rulers to executions. I don't think it implies that King Elessar would never have someone executed, or allow someone to be executed.

As for Eol - I don't think the Elves were shying away from bloodying their hands. Being thrown from a cliff was probably considered a terrible way to die - and a shameful one, for there would most likely be no burial. It may be also... that there WAS hesitancy to have his blood on anyone's hand, but only because he had married the King's sister, and was thereby connected to the royal family.

[Willow Oran]

As for Eol - I don't think the Elves were shying away from bloodying their hands. Being thrown from a cliff was probably considered a terrible way to die - and a shameful one, for there would most likely be no burial. It may be also... that there WAS hesitancy to have his blood on anyone's hand, but only because he had married the King's sister, and was thereby connected to the royal family.

I agree with you that being thrown from a cliff probably was considered terrible and shameful and that Eol's kinship by marriage to Turgon probably was a factor.

However, these are elves in whose cultural memory violent death plays a hugely traumatic role. The very idea that an elf could kill another elf for any reason would have been fairly recently introduced in an elvish view of time and the oldest generation of elves likely to be found in Gondolin would still have been coming to terms with it. What's more, they would have directly linked the idea of killing their own kind with being severely punished themselves - through exile and a very real curse on their people.

If secrecy hadn't been a necessity, it's possible that Eol might have been allowed to live, with the idea that having his son taken from him to live amongst a culture he hated, and the guilt of having killed his wife, would be punishment enough.
Since the need for secrecy made booting him out of the kingdom impossible and keeping him permanently locked up or enslaved (ala a thrall of Morgoth) would have been even more distastful, they compromised by executing him in a manner that allowed some delusion of not having spilled his blood and therefore not being as bad as the kinslayers.

[Valandil]

If Elves were willing to kill innocent Elves in a Kinslaying, I think they would have no problem killing guilty Elves (those with Elf blood on their own hands) via execution.

[Alcuin]

I think the problem with Eöl was that he showed no remorse after murdering Aredhel. (He wanted to murder Maeglin, missed, and killed Aredhel by accident: it was still murder.) Elves were generally merciful, I believe: Tolkien says that they showed mercy to all creatures that surrendered and pleaded for it, except Orcs. Presumably Orcs had shown themselves untrustworthy in this regard, willing and ready to kill their merciful captors at the first opportunity.

In other words, as soon as he was able, Eöl was willing to murder again, and he was unwilling to abide by Turgon’s rule that anyone who knew the way into Gondolin had to stay there. The whole problem arose when Aredhel broke this injunction; regardless, Eöl basically showed himself no better than an Orc: willing to murder again, unwilling to abide by the law that was placed before him regarding residence in Gondolin, and in particular, unrepentant about killing Aredhel. It was dangerous to keep Eöl alive, and having earned a capital sentence, he received it.

Now, whether any of this entered into Tolkien’s calculus in determining the outcome of the character Eöl in his stories, I cannot say.

But there were other Eldar who were equally bloodthirsty. Fëanor and his sons were notorious. Celegorm and Curufin tried to murder Beren and kidnap Lúthien; and it can hardly be expected that they had good will toward Lúthien. Maedhros and Maglor murdered the guards of the Silmarils at the end of the War of Wrath, but Eönwë forbade their execution.

Perhaps this last incident says much in saying little: that Eönwë forbade the execution of Maedhros and Maglor despite their cold-blooded murder of the guards says clearly, I think, that all the Eldar, as well as the Maiar, recognized capital punishment as a legitimate means of addressing the very worst crimes.