I'm not sure it does make things fairer though. It's too one size fits all.
In my area like i said, we now have 3 bed flats that no one will move single people or couples in to because of the bedroom tax - But only ground floor ones will go to families, because they don't allow families with children under 12 to live in 1st floor + flats.
Obviously people with children over 12 can move in to them, but then once they've left home the parents will have to move, eventually there will just be a load of empty flats because there won't be anyone eligible to move into. I've lived in emergency housing etc and most people in them have younger children, i've never known anyone in one with older children - These people will get 2/3 bed houses.
Surely you'd rather see someone in need get it, even if it might be bigger than they strictly need, than it sit empty and rotting? What is the point in that?
My mum lives in a housing association property too - She was quite happy in her 2 bed flat. It was perfect with her mobility issues, being ground floor. She asked for help with the homophobic, violent neighbour who kept attacking her and her partner and poisoning my dog when we were there, and their only solution was to move HER. I don't think that's very fair that she will end up paying because of a violent criminal and the authorities refusal to boot him out.
Not only that but like i said, Judging by number of bedrooms alone is silly to me. My first house was 2 bed and it was bigger than most 3 bed, every room was massive, i had a massive, secure back garden. Someone with three children could comfortably live in that house, i'd even say 4 in fact, if they were all the same sex or young enough to share and not be overcrowded, yet i've been in 3 bed houses that i would feel cramped in with two children.