You also want to gather references on expert opinions on why govt should continue invest on space program (as opposed to only hoping private sector do things). My personal opinion on this is that private sector is driven by profits and space is more of a scientific/academic research innately driven by our need to explore. There would be several areas left untouched and/or won't be attempted if govt pulls out its effort (such as private sector would have little or no interest on doing Hubble telescope or probing in to deep space or measure background uwave radiation with high precision). This is very similar to what's happening in several other areas like medicine research where private companies are folding research which is otherwise pure scientific curiosity or only has long term perspective but have no direct profitable opportunities in short term.
Again, these are not the data points you need to invent. I'm sure these are well documented by expert on this subject. The petition's task should be to gather them at one place and bring public support for it. Without doing this home work, this petition is pretty juvenile and does not have much of a backbone.
As for private sector space, though much of it is currently driven by profits, my thoughts are that if the private sector can lay out an infrastructure to make it easier to access space, then the scientific community has more of a capability to continue research at a lower cost. This is the same idea of how NASA is continuing to send supplies (and eventually astronauts) to space through SpaceX. Eventually, NASA won't have to spend as much on transportation costs, because the private sector will have made reaching space cheaper. Or at least here's to hoping!
