Chaser is qualified my monetary loss; more precisely someone who benefits of another person’s property at the expense of the owner’s profit. E.g. if you rent out a house, and I go in, and no-one else can stay there because I am there, I have caused you the loss of rental.
If no-one else would have stayed it is called lo chaser, and the owner cannot claim payment.
As for your question whether it is ‘moral’ to be nehneh, I think you are asking whether it is permitted l’chatchila (ab initio), if so I refer you to the Gra on C.M. 363, Nesivos 250,16 and Shut Chasam Sofer Vol. 5 (C.M.) 79, the Pischei Teshuva in C.M. 359 and even in the Rishonim: Tosfos Rid on B.M. 117b.
I discussed this very issue with R’ Zalman Nechemia Goldberg (R’ Sholmo Zalman’s son-in-law, who said about him that he is the world expert in Choshen Mishpat and Even Ho’ezer) on a number of occasions, and he rules that it is permitted l’chatchila.
That is all on the premise that the owner does not stipulate to the contrary (see Tosfos and Rema) – if a person makes a ‘machaa’ then the nehneh transgresses gezel. If it is clear that the owner would not want someone using his property, even without stipulation this may be enough to constitute theft.
See the upcoming article in the Yated Neeman in a couple of weeks which will discuss this issue in Rabbi Travis’ QandA with the Gedolim column.