I replied to your comment because I agree with you but I couldn't find any information online to support it. I cited research where they studied foam that's been in place for 40+ years and it's fine. I was hoping you had data that would support what we both want to hear.
What is a "long time"? Is it one human lifetime? The time period in which these blocks will be a blight is a whole lot longer than the time period where they make a nice landscape, it's just that the nice landscape part comes first. Should we do anything we want assuming that what happens after we're dead is irrelevant?