> Pesticides are not enough to explain all the harm to bees.

How do you know this? Because of the possibility (and it will always exist) of something else able to harm bees we should take no action?

> "we don't know how to save all the bees"

Is this forgone conclusion? Sounds like you are begging the question [1]

I am reminded of, http://i.imgur.com/couhw4k.jpg

[1] https://en.wikipedia.org/wiki/Begging_the_question

I'm not saying the bees will definitely die off. I'm saying we don't know. We need to be prepared in case it happens.

Edit: I definitely didn't say that we should take no action.

Edit2: If you're asking "what else has been killing bees en masse", here's a list: https://en.wikipedia.org/wiki/Colony_collapse_disorder

I am sure we agree, just not the delivery.