I think "dangerous" is probably a bit too strong of a word. But they make for lousy handling. It does depend on how the car is set up, but you have to be much more careful about ride height. If you lower the car at all from the stock specs you'll constantly be on the lower bump stops. More than you might think too, because the lower bump stops are progressive so it's not a big hard hit every time. I have literally told someone on this board that their lowered car had to be sitting on the bump stops the way it was set up. They didn't believe me. But when they checked, they'd be been driving the car with it literally sitting on the bump stops for years.
It just really reduces your handling ability. The body roll is severe. Any hard inputs like slamming on the brakes also causes the suspension to bottom out, which again lowers your chances of maintaining traction. If all you do is putt around, maybe it never comes up. But if you have to avoid an accident and try to turn sharply you'll bottom one side of the suspension, lift the opposite rear, and roll the body at an extreme angle in between. All of which reduces your traction, your ability to stop, and your ability to avoid whatever it was you were trying not to hit.
Worn out suspension is less capable than properly kept suspension, yes.
But I think you believe that as the spring gets old the spring rate changes, and that's not really true. The spring rates of all springs is set by the metallurgy of the steel itself. All springs tend to "sag" over time, they lose some of their shape. But how that effects the suspension depends on the spring. Like a leaf spring just gets flatter. That lowers the car, and depending on the shape and how the leafs are laid out can also change how the spring works mechanically. But normally it doesn't lower the spring rate substantially. When a coil spring sags it also lowers the car. But, because of the shape of the spring it also means the coils get closer together, and that increases your chances of coil bind. The spring rate also doesn't typically change much though, the metal itself is the same thickness, the number of coils remains the same etc...
With a torsion bar, the car just gets lower to the ground. The "sag" come in with how the hex ends are clocked, over time the hex offset changes and the car gets lower. But there's nothing to alter the spring rate. If you raise the car with the adjusters you maintain the same suspension characteristics. The issue ends up being that eventually you run out of adjustment and can't keep the car at ride height.
Yeah, I think "dangerous" and "unsafe" are pretty strong words.
But if you think the handling of a car running radial tires on the street with /6 bars isn't bad enough to negatively effect your ability to avoid an accident, you're sadly mistaken. Those /6 bars had too little spring rate from the factory, even for a /6 car. Up the weight, add radials, and those light bars will negatively effect your ability to stop, steer, and maintain the traction you need if things get sketchy. It doesn't have to be a race or an autoX, and it doesn't matter how safe or experienced you are as a driver. **** happens, and when it does you will not have the handling ability you're going to want.
