FreeBSD is too filesystem errors sensitive

[cronfy]

Hello.

Please forgive me for probably a very stupid question. But why is 
FreeBSD so sensitive to filesystem errors that it ends up with panics 
like 'freeing free block' or 'ffs_valloc: dup alloc'? I just can't get 
it. Failed to allocate vnode? Go allocate another one! Freeing free 
block? Leave it free then! I understand these situations should never 
happen, but the hell why is it required to panic and kill everything 
that would be working happily even if something very disasterous happen 
to /backup partition, in example?

Would be very appreciated if someone could explain that... thanks.