They were social outcasts after they fell in love, and they brought about revolutionary change first by Luthien becoming mortal, second by introducing a mixed Eldar/Maiar bloodline into the gene pool of the heroic caste, and third by shaking up all of Beleriand by their victory over Morgoth and inspiring the great, renewed alliance against him (the Nirnaeth). That alliance came to a bad end overall, and specifically led to the curse on Hurin's family, but revolutions often don't always turn out well.

The romantic hero is different from the modern heroes we tend to think about. The romantic hero is either raised outside of or cast out from society. He or she always follows their own moral compass in defiance of a conventional society which is either amoral or unjust. Society views the romantic hero as a threat and rejects him or her. The romantic hero follows his/her own moral compass in defiance of society and eventually is destroyed by the flaws in their personality.

...and...

Promethean type characters were used in the 19th century as a harbinger of change.

...and...
a Promethian romantic hero's chief characteristic is defiance of all authority. He or she is convinced that society or even God is wrong and is unwilling to concede even an inch to compromise with forces he/she feel are wrong. This is the source of their immense power and allows them to do things that no other mortal could achieve but it is also usually seen as a tragic flaw that is the seed of their own destruction.

...and especially:

My question is how does someone with right wing reactionary tendencies such as a Tolkien take to the Prometheus legend?

His wrath and his hate were given most to Morgoth, and yet well night all that he said came from the very lies of Morgoth himself; but he was distraught with grief for the slaying of his father, and with anguish for the rape of the Silmarils'.

'Why, O people of the Noldor', he cried, 'why should we longer serve the jealous Valar, who cannot keep us nor even their own realm secure from the Enemy?'

Perhaps knowing that we cared about the Elven kingdoms, in the adaptation, Tolkien took advantage of our sympathy to increase the scale epic? How much fall out is there in the Kullevero? If it is more self-destructive, perhaps the reason was that we only really know a few people, and the harm to them would be more felt? Reading about a tragedy become a lot more real of you are emotionally invested. Yes, I think that's a great summary Rem, and one reason it works is because of something we have discussed about JRRT: the true love of his subject and his world. I think that comes through, in this tale, because of his real attachment to the Elves and to Arda. And the effect Turin has on those who would otherwise be immortal really resonates with us, as mortals, and to whom the idea still likely holds a fascination.

Also, (though this should probably wait for the COH read-through) I think I see twos eps of tragedy: the wide, Beleriand spanning destruction in the fall of kingdoms and powerful people, but also the personal destruction of Turin's soul. Does the Kullevero end with suicide? Indeed we will cover this more - Kullervo ends his life on the sentient blade which he has used to slay his enemy and his family in his quest for vengeance. After Kullervo slays Untamo (who destroyed Kullervo's early life) he returns to his home to find his family and tribe all dead - including a maiden that he casually had a liaison with, and whom he now realizes is his sister; she is dead by her own hand.
No Second Prophesy for poor Kullervo. The Finnish god/wise man/bard Vainamoinen completes the tale by advising that children should be loved and not sold or cast out, for without love and wisdom they may turn dark and commit deeds like Kullervo.

Perhaps they are those overly ambitious to match the unnatural suppression and injustice, and the ones who self-destruct are those unable to dial it back to match the normal levels, and they go too far to one extreme?

I could not tame my nature down; for he
Must serve who fain would sway—and soothe, and sue,
And watch all time, and pry into all place,
And be a living lie, who would become
A mighty thing amongst the mean, and such
The mass are; I disdain’d to mingle with
A herd, though to be leader—and of wolves.
The lion is alone, and so am I

Well, though it torture me, ’tis but the same;
My pang shall find a voice. From my youth upwards
My spirit walk’d not with the souls of men,
Nor look’d upon the earth with human eyes;
The thirst of their ambition was not mine,
The aim of their existence was not mine;
My joys, my griefs, my passions, and my powers
Made me a stranger; though I wore the form,
I had no sympathy with breathing flesh,
Nor midst the creatures of clay that girded me
Was there but one who—but of her anon.
I said, with men, and with the thoughts of men,
I held but slight communion; but instead,
My joy was in the Wilderness, to breathe
The difficult air of the iced mountain’s top,
Where the birds dare not build, nor insect’s wing
Flit o’er the herbless granite; or to plunge
Into the torrent, and to roll along
On the swift whirl of the new breaking wave
Of river-stream, or ocean, in their flow.
In these my early strength exulted; or
To follow through the night the moving moon,
The stars and their development; or catch
The dazzling lightnings till my eyes grew dim;
Or to look, list’ning, on the scatter’d leaves,
While Autumn winds were at their evening song.
These were my pastimes, and to be alone;
For if the beings, of whom I was one,—
Hating to be so,—cross’d me in my path,
I felt myself degraded back to them,
And was all clay again.

From childhood’s hour I have not been
As others were—I have not seen
As others saw—I could not bring
My passions from a common spring—
From the same source I have not taken
My sorrow—I could not awaken
My heart to joy at the same tone—
And all I lov’d—I lov’d alone—
Then—in my childhood—in the dawn
Of a most stormy life—was drawn
From ev’ry depth of good and ill
The mystery which binds me still—
From the torrent, or the fountain—
From the red cliff of the mountain—
From the sun that ’round me roll’d
In its autumn tint of gold—
From the lightning in the sky
As it pass’d me flying by—
From the thunder, and the storm—
And the cloud that took the form
(When the rest of Heaven was blue)
Of a demon in my view—