Sorry, but the main argument from Solo players, saying they don't want to interact with other players ever, is quite ironic considering that many of them post quite a bit on these forums. Hey, if you don't ever want to interact with others, then you'd better not ever go outside, ever go the the store, or ever get a job. Guess what? They are PEOPLE there that will try to interact with you regardless of if you want to return the favor. Also, there is a small risk you might be robbed too, or someone might rear end your car while driving. Does this stop any sane person from leaving their house? No, of course not. If your answer is yes, then go please seek a psychiatrist, because that's not normal and you need help ASAP. Before someone tries to make the silly real life != game argument, this is a SIM, and I want it to play that way.
A game that allows players to play in essentially the same server but allows then not interact with one another is not an MMO, period. If you are able to play the game without interacting with others players ever, you are not playing a multiplayer game, period. You want to play in Solo mode to learn how to play the game, or try certain things without the risk of doing it in 'live'? Fine, but any achievements/money/ships you obtain should not carry over to 'live.' The fact that the game is the way it is now due to this whole catering to everybody mentality is what is keeping most good games these days from becoming great games, and this is one of those situations.
Normally, I always play in Open mode. But recently I wanted to try trading, and that's when I learned the ridiculousness that is Solo mode since I could trade with less risk in Solo mode (and hence gain more money). So that's what I did, so I could gain as much money as possible to buy the ship I wanted without interruption (pirate NPCs are a slight annoyance, nothing more). But I wish I didn't have that choice, because it made the game more dull and uninteresting. Yes, I could have done this in Open mode and not have ever been attacked by another player, but the small chance was there and that makes the game more exciting. People will always go with the path of least resistance if given the opportunity. Why would anyone study hard for a test if everyone was guaranteed an A? That is an extreme example, but the point still stands. Maybe the risk in Open mode is only slightly more than in Solo mode. Doesn't matter what the metric is, just that fact that one has less risk is all that matters.
But the worst reason for these modes is it splits the community up further in the game. It's bad enough that this "MMO" is instanced, because that splits up the player base. But now you want to split it further into those who want to play Solo and those that don't? If you are a trader, you would have to be an idiot to play in Open, because it adds risk with no real benefit. This now ensures that being a pirate is no longer a realistic option as a player that wants to play a multiplayer game. This in turn makes it no longer a realistic option for someone who wants to be a bounty hunter in a multiplayer game. This in turn makes this supposedly multiplayer game into a game where each player is playing solo among other solo players. This kills the game.