Where did they say they wanted to block ships ? All I've seen is that they wanted to film & document the ONG's activities, to see if they are not engaging in human trafficking.
See https://youtu.be/YmcK6GvgVPs?t=3m27s, Patreon's presentation of evidence that they were blocking ships, and that Southern was actively involved. Note that this evidence is video that Southern herself published before she realized that these actions would endanger her own income stream, rather than just people in the ocean.