I can understand
Thingol in his reluctance to have closer contacts with the
Noldor.
First - he had not been eager to cross the seas and follow the others at the time of the great march of the
Elves. The beauty of
Beleriand was the first "enchantress" he had met even before
melian. Melian herself had chosen to dwell in Beleriand and not on the immortal lands.
All of a sudden, there come thousands of elves, ones from another house, all shining with armour, valour and "that" flame in their eyes...
Wouldn't have the much "simpler" king been reluctant to meet them? He would have.
Second - The hosts of the
sons of Feanor and those of
Fingolfin, coming from the North, were numerous, and accompanied by the first rising of the Moon and the Sun, and the victorious
battles in the very first days in ME against
melkor and his
armies........ That could have given quite a thought to
the wise king
Elu-Thingol.
To openly state hostility? -
Unwise! They are much stronger than me and my scattered and free people!
To openly welcome them? -
Why should I?! Soon they might become mightier than me!.
To refuse them as his neighbours -
Unwise! They are too many and too strong. Let them now fight the Enemy and his orcs while I, Thingol, will be safe in here!
Those I see as possible and more logical reasons for Thingol's behaviour towards the newcommers.
But ithrynluin, IMO, he did not know anything about the kinslaying. He and his Maia-wife could have possibly sensed there was something wrong.... but as far as it is known, by the time of the first kinslaying there had not been ANY other similar case known among the Eldar. Elved had been killed by Orcs and other
creatures and
servants of Morgoth, but untill the kinslaying no
Elf had ever killed another Elf. Right? Thingol, nor Melian, could not have even guessed that THAT was the main curse and the hidden shame of the Noldor that could be somehow perceived.