I don’t think sampling without permission is ethical. To me, music that someone creates is something that should be treated with great respect; it is something that the artist put many hours in until they got it just how they wanted. I view sampling it without permission as to be disrespecting the amount of work they put in, and it also seems kind of lazy.
However, I would only view it as such if the person sampling didn’t put much effort into their new track. If I take the drum beat from one song, the guitars from another, and then a bass part from another song and call it my own, did I really write a new piece of music? It’s new in the sense that those combinations of loops didn’t exist before I put it together, but how original am I being?
On the other hand, if I were to combine many samples, and also add some of my own original material, then I would view it as a new, original piece of music.