Basically what your post comes down to is a rehash of the "I don't want there to be a Solo option, everybody should be forced to play with me"
Not everybody does.
You can't force people to play with you if they do not want to.
There are enough player killers/griefers and other idiots around to completely justify the Solo option.
I play mostly Open, but I have watched many videos that made me wary of fellow players and I have quite a long list of CMDRs that I will never trust.
If everybody played the pirate roleplaying game the proper way I bet many more CMDR's would try Open.
I think there is an important place for true player pirates in the game and I feel they add a lot to the atmosphere of the game.
Alas, I have been attacked several times myself by CMDRs that did not communicate at all, but just wanted to kill another player.
You should blame them for CMDRs going solo if they have a lot at stake.
If ED had had an offline option (I understand why it currently does not) you would not see most of the CMDRs that play Solo in Open either.
I believe you see more in Open now than you would have, if there had been an offline option.
I myself for example would have not even considered playing Open, but now I do 95% of the time.
Do pirates hide in solo?

If yes, then you should blame the pirates and not the traders.
If no, then your reasoning is flawed.
You seem to suggest that pirates will only be pirates if they can pirate other CMDRs?
If that is true then one should ask why that is the case.
But the same thing applies: If people don't want to play your game, then they don't.
If there had been an offline option you would not have encountered most of these players either.
I am not a pirate myself, but I suspect that another reason could be that there are too few NPC with interesting/valuable cargo?
I remember this being the case in the early days. I don't know if this is still true. This could be easily remedied by FD.
This is nonsense too.
If people want to play with other people then they will play in a private group or in Open. If they do not then they do not.
I play in open. Currently I trade in a Cutter with a cargo of approximately 10 mil credits. I still would not accept human escorts.
I play solo even when I am in Open!
You can't force people to play your game.
It is that what you seem to want to do.