[Sharkû]

Elves are, not least due to their stay (at least of some leading persons of them) well aware of the privileges, abilities and attributes of their race. As Iluvatar is said to have put it, they are the 'fairest of all earthly creatures' (Silm, 1). No elf, even if he could be considered a rebel or be accused of nefarious deeds, would, on the other hand, see himself as truly evil. The majority of the elves remains unfallen, the others for the largest part had their reasons for their actions, too, even if they were directed against the Valar. The nobility, splendour and beauty of elves therefore is dialectical, both objectively – as concepted by Iluvatar and witnessed by the Ainur – and subjectively, manifested in their arrogance, longing for a changeless, status quo-preservation, and sometimes, their self-righteousness.

Likewise is the nature of Man, and how the elves see it. In the Silmarillion, Chapter 1, we have the straightforward sentence
'Yet the Elves believe that Men are often a grief to Manwë, […] for it seems to the Elves that Men resemble Melkor most of all the Ainur […]'.
Of course they are to a considerable degree right with that assumption, as only men ever had multitudes serving (more or less willingly, though) the Dark Lords. The understanding of nature, the way of life and the metaphysics which the elves possess both from their education in Valinor and also apparently intuitively, is not compatible with the actions of many of mankind.
Here the fate of men is also important to be taken into the scheme, as it poses not only one reason for their estranging from the elves, but also often serves as a logical explanation of the behaviour of Man, whose point of view is limited to their short lifespans and to a past traditioned rather in rows of ancestors and the tales of their doings than in actual memory as is the case with elves.

The question to what degree the emnity from the elves towards the Strangers is justified naturally arises. Of course, there is enough emnity working the other way round, as is shown in all three ages, be it the alliances of Easterlings with Morgoth, the mistrust of the men of the King of later Numenor towards the elves, or the image of Lothlorien we see in Rohan and Gondor. On the other hand, one would have to argumentate that the elves as the side which has more insight, and more foresight as well, may not exact likewise sentiments on the men as they do on them. With a differentiated approach, the actual emnity of the elves seems questionable. Protection from harm is justified, and sometimes it was not only the elves protecting themselves from men, but also them lending aid to them. The fact that military aid, for example, was practically always denied with the arguments that the elves had own affairs to deal with, even though they had previously received mortal reinforcements in likewise situations, is a different topic.
Conclusively, there are a good number of reasons for the elves mistrust of the Atani, and most of these reasons work the other way round, too. What justifications both sides have is something else; one might argue that the one who exacts more emnity would have to have the better reasons as well.