Count me in as another angry backer who was looking forward to offline more than online.
For everyone saying, "If you don't want to be affected by other players, just play solo!", have you considered that FD is forcing everyone to be online precisely so that the actions of all the other players will affect the entire gameworld? They said it themselves, they want the galaxy simulation to be driven by player action.
Being "affected" by other players is a lot more than just avoiding player pirates and unwanted dogfights. Found a sweet trade route that you want to exploit? That's great, but if you log off and then come back a few days later when you get some more time to play, there'll be dozens of other players who will have found it and flipped the market upside down because, surprise, FD is forcing you to use the same market simulation as all the open-play people.
Want to go exploring and make your fortune as a deep-space explorer? That's great, but you better hurry up because the explored-system database is going to be getting filled up with the thousands of other players all expanding outwards at the same time, so when you come back to the game after a week of working long hours, that stellar cluster you had your eyes on will already be fully explored.
Want to become a big asteroid miner, searching for that elusive motherlode of valuable ore? That's great, but when you find that asteroid belt glittering with riches you better hurry up and mine it as fast as you can before someone you never see or interact with in any other way comes along and mines it out from under you.
THAT is why people are upset about no offline play (not counting the thousands of people who have legitimate connectivity issues, because not everyone enjoys a First World always-on broadband experience). THAT is what people are talking about when they say they just want to play by themselves and not have to deal with other people. All "solo online" mode achieves is removing the ability to get your ship blown up by other players. You'll still be dealing with them in every other way.
Honestly, I have to wonder if all the people talking about how "Kickstarter isn't a guarantee" and "game development is hard" would be so glib if instead of trashing offline play, FD had come out last Friday and said, "Hey guys, we really tried, but it looks like the game will only work with a maximum of three players per instance, sorry" or "We did our best, but the game engine is only going to allow a maximum of four different ships in the game ever so that's the decision we made."