Some good points in the responses that highlight the issue.
I am not an "open only" person - I think everything in the game should be doable in solo mode (perhaps with the exception of powerplay). If you want no interaction with other players, that's fine.
Firstly, what I'm trying to address is that people go into solo for the wrong reasons. I suspect many people would like to play with others, see other players, and have some opportunities for co-op. But because of fear of gankers, they skip that opportunity altogether.
Secondly, regarding solo vs open incentives, as an example there are certain BGS and powerplay activities that really mess up the balance. For example, if solo or private group players engage in combat activities against a player faction, there is no way to counter them. If a solo player goes into a system and starts indiscriminately killing clean ships of a certain faction, there is no way for players in that faction to retaliate. I don't know about you, but this seems like cheesing the system. I am not proposing to eliminate solo mode altogether as that would be an extreme solution...instead, perhaps reduce the negative effects of their actions if they are in solo. If negative faction effects were reduced by 50% in solo mode, then that would at least provide an incentive for the pilot to do it in open.