One of the trickiest things for a facilitator is having an opinion...
...and holding it in.
The ethics of this situation are tricky.
It is not that I never share my opinion, but I often find myself kicking myself for doing so. The tenor of the session may change. People can look upon me as partisan. I may 'get in first' with my opinion, shutting down dissent or turning off the tap of creativity. When I start playing another part, the session can drift, rudderless.
I don't really know what other people are thinking, but I do know that I was not invited to facilitate so I could have a forum for my own opinions.
Back to the facilitator holding in that opinion:
You feel like you could burst.
You remind yourself of the last time your opinion leaked out. And tell yourself it wasn't so bad.
Hold on. Just hold on.
Write your opinion down, and fold the page over, so people cannot casually see it.
Whatever you do, hold the line. You are the facilitator.