As for concurrent systems being harmful, you just have to design your program for threading in mind. Minimize shared state and be very careful when you can't.
Better than time wasted debugging the races and deadlocks that only threads can cause. These are much harder to debug because they are so much harder to examine without changing behaviour.
Sure, there's a trade-off - so there's no point in pretending that there are no downsides to using threads.
