Police union upset for being called out on something that police have done at other protests

Police union calls for Sid Ryan to resign over ‘inflammatory’ comment - thestar.com
The police union is upset that Sid Ryan suggested that the police might plant undercover officers in the G8/G20 protest crowd to incite violence. It is something that has been done (and caught) at other protests, including a 2007 protest in Quebec.
I think, instead of the police union getting upset, they should reassure the public that they won't be involved in such practices. I think it was actually responsible of Sid Ryan to bring up this issue so protesters will keep an eye out for people stirring up trouble and thus avoid adding to the trouble at the protest.