air bricks/ insulation and wooden floors

[navigator1952]

i know you need airflow under the wooden floor to stop damp/rot etc.in these days of high fuel prices it set me wodnering....why cant i fill all the space under the the floor with insulation then no drafts no heat loss lower bills. job done.
the insulation stops rising damp, stops condensation and prevents rot.there is no free air in the space to warm up or cool down so there no need for ventialtion for the joists which are warm and dry?
please tell me if i am wrong.