The more wrong a speed limit is, the more dangerous it becomes. If it's 30 where I can safely drive 50, I have to keep my eyes on the speedometer to not speed and get a fine, which makes the road less safe.
You should be aware of your speedometer even if you think you can safely drive at a speed......
Especially in urban areas, where I'd assume it's more likely in urban areas for your car will collide with people at no fault of your own, like a kid carelessly running onto the road. Lower speeds make crashes far less dangerous, I wouldn't be surprised at all if five 30kph crashes a month had a significantly lesser fatality rate than one 50kph crash a month.
edit: very relevant, someone else mentioned this video. Amsterdam set their speed limit down to the same 30kph.
There is logic to this. Things can be done to make a road feel like it should be slower. Eg, if it's 2 wide lanes in a straight line, that road can feel like it should be 70 or 80. By making roads appear narrower, for example, can subconsciously signal that we should be going slower.
I have driven a lot around the Netherlands. It's pretty great. The only places with bad speed limits there are the highways. All the rest is very well designed and often doesn't even get you to the limit.
No. Not at all. I don't feel the need to speed. I just drive at a safe pace, which is often faster than the artificial limit they have put somewhere. (Which they often do just to make money from fines)