Your point of view speaks of your limited perception regarding things happening in the world.
First of all weight reduction on cars is not done at all to increase speed and acceleration, yes it is done on sports cars but on daily drivers. Weight reduction is solely done to save fuel and fuel my dear is a thing that we will not get again in this world no matter what ever we do so we people have to conserve fuel for future
How on earth can you say that these modern cars are tin dabbas. Leave suzuki and take toyota and hondas. My dear these tin parts are used because they are flexible and upon impact their flexibility absorbs all the shock and thus lesser damage to the main frame of cars. You just said what ustaads here say. I think you have not been involved in an accident with these modern day cars so you can not think of that way but I have been involved in one and tell you what if it was a car from 80's I would not have been typing this message here. Tell me how many cars of 80's had side impact bars in doors and one big solid bar under dash board. There metalic bumpers used to bend the entire frame upon impact.
Newer cars are made with one thing in mind that is safety, all the parts they have are made flexible enough so that they absorb most of the shock of the impact in collision.
One thing that I can say here is that newer cars do not have real good drivers that old unreliable cars of 80's had thats why so many accidents and cars getting more and more damaged and more casualities. If you are brave enough take a 80 corolla and a 2012 and bang both of them on wall at same speed. You might notice more cosmetic damages to the 2012 one but once you strip all the garbage off the frame would simply be undamaged. But when you strip off a 80 one you will notice some damage to the frame as well.
We all have to change our mind set that thicker a thing it is it will save us from damages, but I dont only few know that carbon fiber being thinner than metal can be stronger than metal in a collision, but we illiterates dont want to know whats going around in the world we just believe what someone says.