"If you push them too far you'll drive them over the edge. It doesn't help our cause one iota."
Misinformation surrounding the use of 1080 was exasperating, he said.
"There're a lot of incidents that we are not being told the whole truth about and it seems to me that the little things don't matter in the big picture when they should.
"I don't condone what they've done but if there was a bit more honesty out there, then ..."
Martinborough 1080 opponent Bill Benfield, author of The Third Wave: Poisoning the Land, said sending the letters was a dumb move.
"I was fairly annoyed. It's pretty stupid, it's not the sort of thing that helps anybody.
"I think the letters are stupid but I also think the Government throwing 1080 all over the place is stupid too."
None of the 1080 opponents he knew could be responsible, Mr Benfield said.
"I don't know anyone stupid enough to do it. It's far more likely to come back against the 1080 movement."
He believed it was possible the threats had been made by someone outside the anti-1080 lobby.
"Until we know we can't exclude anyone - and we don't know."
If a 1080 opponent was responsible, however, they had done the cause more harm than good, he said.
He had not been contacted by police, although several 1080 opponents he knew outside the district had been questioned.
Meanwhile, a forensic psychologist at Massey University said the perpetrator could be someone whose pet had died from 1080 poisoning.
Dr Mei Williams said the perpetrator was likely acting from a personal rather than a political motivation.
"They may have experienced a beloved animal die in severe pain from 1080 poisoning - hence the anger towards the authorities and the desire for revenge. For this reason, I don't see it as a group but rather an individualised act.
"For some people, pets are like family, or the pet is a like a baby or child. To lose a pet in this way, especially where there is a strong attachment, could fuel extreme emotions and lead to anti-social behaviour."
She disputed the use of the term "eco-terrorist" saying the term had honourable implications.
"There's nothing honourable in what this person has done."