How strong are switch blade knifes? if held point blank and deployed will they even penetrate though a sweatshirt?

In a typical switchblade, the blade is sharpened only on one edge and swings outward in an arc, with the dull edge leading. These are specifically designed not to cause harm as the knife opens. If the knife was positioned at just the right distance, a person could be scraped with the point as the blade swung open, causing a superficial cut or scratch.

Other designs hide a double-edged blade entirely inside the knife handle, which springs outward in a straight line when deployed. I have seen versions which will only deploy the blade, which must then be pushed back into the knife body with the switch held down, and I have seen versions that both deploy and retract using the switch/button. In the former, a stronger blade means that a person would have to work very hard to retract the blade, and would likely damage the knife while doing so. In the latter example, the person's thumb has to overpower the springs or mechanisms in order to retract the knife, so a strong spring would make the knife impossible to operate.

Switchblades were originally banned not because they were any more dangerous than regular knives, but because they were scary. Gang members (mostly of the Hollywood variety) would carry switchblades and butterfly knives, and would make a flourish of opening them in order to scare victims. This probably rarely happened in real life, and was mostly a product of movies.

The same thing is happening today with guns. More often than not, guns are not banned by how powerful they are, but how scary they look. Again, this is largely based on Hollywood stereotypes. This is why a shotgun with a barrel shorter than 18" is a class III firearm (like machine guns, etc.), but you can buy a revolver (pistol) over the counter that fires shotgun shells and has a 2" barrel that can be concealed in a pocket. "Assault rifles" have scary pieces of black plastic on them and look like military weapons, so they must be powerful, right? Nope. The 5.56mm/.223 cartridge that 90% of them use fires bullets the same diameter as a .22 rifle (.223"), and was specifically designed to be less lethal in combat. The idea is that it is more effective for a soldier to wound an enemy than to kill him, so that extra resources and personnel are needed to drag him out of battle and help him recover. Incidentally, those rifles replaced .308 and 30-06 rifles, which are the rounds you'll find in your dad's hunting rifle. Those are also military rounds, and were most certainly designed to kill! But, an old hunting rifle with a wooden stock doesn't look scary, so nobody is trying to ban them.