The point is that there is no cluster in thingspace referred to by the word
This is debatable. I believe there is -- it's just that the word is so convenient for propaganda, it is routinely hijacked.
It's not just that. For a lot of people it's convenient to apply the connotations of "terrorist" to everything besides actual terrorists, e.g., the AP is perfectly willing to call the UKIP or Tea Party "terrorists" while refusing to call groups like Hamas terrorist.
This is similar to the way the US government has declared war on poverty/drugs/cancer, while calling actual wars "kinetic actions".
Another month, another rationality quotes thread. The rules are: