If they are posting objectionable articles in their wall that appears in your feed, if you go to that upper right corner and mouse over the dropdown arrow you'll see several choices, including blocking the party whose post they are forwarding. So if your friend ABC123 is sharing posts from XYZ987, you can block XYZ987 without blocking your friend. When your friend shares more from XYZ987 it won't appear. I've done that with a couple of my oldest friends from my home town. We have a lot in common, but politics isn't one of them. This lets me keep them in view for the other topics we enjoy. I assume they also block my political shares.

SRS