Comment 6 for bug 196453

I think the question you need to ask is the object effectively there?

It is for not effectively there IMO, since it has no solid form, setting it to zero opacity is the same as not being there.
It's more like a ghost than glass. If you can't see a ghost you can't do anything with it. You can do stuff to it(making it show up) when take special measures like you drag select things or tab through the objects.

IMO if you can't see it you shouldn't be able to touch it.

Maybe using layers is a more effective way to do what you want, temporarily hiding stuff.