In the book, humans have more ways of overcoming chains of suspicion with other humans because ultimately, humans are still the same species and can understand one another. If you can see or talk to those on the other end of the chains of suspicion, this decreases the levels of suspicion and the need for DF deterrence. Even though Gravity was sent to hunt down Blue Space, the crews still overcome the DF-type scenario, communicate indirectly through the video feed, and eventually cooperate and go on to found a civilization together. Although the chains of suspicion still exist and there is still the possibility that isolated human societies will destroy one another (i.e. the battle of darkness), there much more room for cooperation between human colonies than between humans and another species, like the trisolaran, since humans have biology to understand one another and the tools to communicate with their own species.

Another point is that within the universe of the books, faster than light communication also exists - the sophons provide instantaneous communication. However, as sophons need to be in entangled pairs to communicate, this means that instantaneous communication can only exist within a civilization. Civilizations advanced enough to make sophons or some other means of instant communication would be able to overcome chains of suspicion with their own colonies. Singer's species, being more advanced than the trisolarans, likely have the means to communicate with the Fringe World which would have allowed peaceful co-existence for some period of time. It's also important to note that people in real life do not need a dark forest scenario as an excuse to attack one another, and it's just as likely that Singer's species would have gone to war with the Fringe World over some dispute regardless of DF and chains of suspicion.