It's as unreasonable as it is effective.
However, to describe a group of people as scum, dehumanizing them for your own political purposes, is much the same.
What are the facts here?
An Iranian citizen is being held in Iran
We know she was working with groups that want to depose the government
We know she has links to the BBC
The fact she's also English is little to do with much. Internet lies, on a larger scale, is how whichever groups spreads a point of view they want people to believe.