As long as they have permission or are only using them for fun and not profit.

Are we talking about sampling or copying here 'cause there's a big difference between the 2, you know. For instance, a song Ice Ice Ice Baby by Vanilla Ice was much more of a copy of a song Under Pressure, not a sample at all. On the other hand, some songs use samples from another song, like let's say Don't Stop The Party by DJ Scotty. It has a music sample from Just Can't Get Enough by Depeche Mode, yet I don't see anyone complaining about that. What can one say about sampling when it comes to a song Crazy For You by David Hasselhoff? It is obviously a case of taking a sample from YMCA by The Village People. I think sampling is OK, but copying is just wrong. Hope I'm not the only one who thinks so.

Why not? There is nothing original any more anyway, not just in music but also on film or on TV! Did you ever watch all those remakes and reboots? That's also sampling to me.

Bearing in mind that it's actually how sampling is supposed to be done and not outright stealing. I've heard a lot of indie artists do this with sounds from not just other songs, but also TV/Film/games etc in pretty effective ways. So long as it's transformative I think it's okay.
Artists and musicians have been borrowing- if not outright stealing- stuff from other artists and musicians for forever and I don't think there's too much shame in that.

As long as that producer isn't copying other artists' exact styles.

It`s fine if the artist is taking the sample and putting it in a much different song than the original. So the new one and original 100% can`t be mixed up and taken as the same song. Like when Madonna sampled ABBA`s song in Hung Up - I knew the original and when I heard Madonnas song, I could recognize the sample, but I in no way thought that it`s the same song. Can`t say the same for many other songs.

As long as they have permission.