The Silmarillion is written from the point of view of the Houses of
Fingolfin and
Finarfin, not that of
Feanor.
There's no doubt that the
sons of Feanor and their people fought long and hard against the
Morgoth. For that, they are to be commended. Doubtless, there were battlefield deeds of heroism amongst Feanor's descendants. I don't know of anyone who could reasonably argue otherwise.
The Kinslaying was dead wrong. Lots of innocent dead wrong. There's no getting around that. They could have built their own
ships. They chose to steal those of the Teleri instead. Why such a hurry? It's not like they'll die of old age in the relatively few years it would take to build such a fleet. And, with a bit of time, they might be able to persuade the Teleri to provide passage.
Instead, they murdered a bunch of Teleri and deeply angered the rest. And what did that get them? They left without the Houses of Fingolfin and Finarfin! They want to go up against the most powerful of the
Valar with only a fraction of the host they've mustered!
So, don't tell me Feanor and his sons weren't capable of being fully, truly, and monumentally selfish AND stupid!
They wanted what they wanted and they simply didn't care what the cost was to others.
And their actions with
Luthien don't show any difference. They wanted to find a way to get the
Sindar into their host. They wanted to control the forces of
Nargothrond, too. They saw an opportunity. They wanted what they wanted and took what they could get away with, again without regard for what others wanted. I really don't see any difference in their methods or intentions, and I see the same weaknesses in their plans due to not caring what happens to others.