While it is true mild steel has a little 'give' to it, these top 2 examples of 10 second 'mild steel' cages gave way too much..... the top one was coming in on the driver and had already failed......

the second pic of a buddy of mines cage also was 'giving' and was a hairs breath away of crushing him when he got into a little (very little) antifreeze of another car that had just run.

It may be hard to see in these pics unless you can zoom in, but both these mild steel cages deflected WAY too much for safety.






This next moly caged car hit and went over the wall at Orlando and disentegrated, but the moly cage did not deflect at all and integrity of chassis was still 100% intact.