[William Cloud Hicklin]

While it's true that the SoF, especially Maedhros, should have acted more diplomatically, it's another matter whether they could. They were under the Doom of Mandos, most especially in any matter concerning the Silmarils and the Oath: "On the House of Fëanor the wrath of the Valar lieth from the West unto the uttermost East...Their Oath shall drive them, and yet betray them;" and I think those were drivers of irrational conduct, an independent dark psychological force somewhat reminiscent of the effect of the One Ring.

(It's also likely the case that, although M&M weren't as crude as Caranthir, privately they too thought of Thingol as a "dark Elf in his caves;" the thought of such an inferior possessing a Silmaril was intolerable to them.)