You don't need flash.. but what do you really need? Food, water, oxygen and the rest is optional. I use Flash mainly for watching live streaming sites on my desktop that provide soccer matches. Granted, those sites are a bit dodgy but there are no other free non-flash solutions.
I will always prefer a non-flash alternative but have no problem using it if there is stuff I like.
Anyone that has doubts about flash security can download a Puppy Linux iso - create a bootable CD or USB. Make sure it will not mount your drives and start it fully in memory. Worst thing that can happen is a reboot. (and if you are really paranoid start it in a VM)


I will not install any version on my N900 though. That just seems like looking for trouble.