Defects in LotR ? (Gasp)

[Sharkû]

As for Aragorn interrupting the Fall of Gil-Galad, JRRT explains in one of his letters (incidentally the very interesting letter where he comments on a LOTR movie script he had been proposed in his life time):

Aragorn did not 'sing the song of Gil-galad'. Naturally: it was quite inappropriate, since it told of the defeat of the Elven-king by the Enemy.

The tale of Beren and Lúthien in turn was one with a glorious ending for both, definitely also more appropriate for Aragorn's personal situation, using Beren as a role model.