How can we know they weren't real spies?
There is a difference between freedom of expression, and cutting a nuclear facility fence. Try to convince people about the dangers of the weapons and not cut the fences.
Cutting the fences will obviously put you in jail. Maybe the sentence was too harsh, but I have little sympathy for them.
If they were detained for speaking about the dangers of nuclear weapons, they'll not have only my sympathy but also any possible help I can give.