ICE is part of Homeland Security, which makes sense because they are the homeland's 'perimeter defense' to some extent, but they aren't solely concerned with finding terrorists, it's immigration and customs.
Should the government have further created more bureaucracy by splitting all of the agencies that were swallowed up into Homeland Security into the parts that directly relate to security, and the parts that don't? Now we need double the boats and double the crews for the Coast Guard and the Coast Rescue agencies...
I'm not necessarily arguing that in this case ICE going after these domains makes a whole lot of sense, but holding onto this, "it's not related to security," angle with a death grip doesn't really do much to progress any type of argument.