There's absolutely no reason to not use acrylic if you don't mind working with it. There's a lot of very soft acrylics on the market now that I find quite pleasant to work with, and with the exception of some cotton yarn, acrylic is the only yarn in my stash. I had some quite old acrylic yarn given to me that the original owners didn't want anymore, and after trying to use it, off and on, for years, I came to the conclusion that it was too unpleasant to work with (and in colorways I don't like, and produced a not-soft finished product) and donated it to Goodwill. That yarn was, indeed, terrible and scratchy and squeaky on my metal hooks and gave me blisters on my fingers as I tensioned it. But newer acrylic is very nice generally. Some brands are really soft and nice, and other brands are not as soft, but softness I think really doesn't matter much for things like amigurumi (and a lot of it gets softer after washing which makes it good for blankets and wearables).
Anyway, it's pretty much just personal taste.