I just returned a cosmetic product I had purchased when I read the label and saw it had microbeads in it. I did not know about the problem with fleece, but will research it. I don't want to use fleece if it is as bad for the environment as microbeads.
This is not just the same-old same-old plastics problem. The problem with microbeads is that they are so small the filters in sewage systems cannot trap them. There are currently billions of these beads in lakes, rivers and the oceans now. It's not just a problem of fish eating them and being deprived of nutrients. These polyester beads actually soak up toxins, so the fish ingest many more toxins than normal. And, of course, it is the small feeders who eat the beads, which then work up through the food chain to mammals who eat sea creatures -- including us. I assume that the problem with fleece fibers is similar.
In any case, I choose not to contribute to the degradation of the environment for things that I know are damaging. There are many excellent alternatives to fleece and microbeads, so it's not hard to act responsibly.