Our building has fire stair door locks that allow access to the stairs from the lobbies and thence to the street – but not the other way round. However, if a fire alarm goes off, the locks all open, allowing access from the stairwell to other lobbies, if required (but I think not from the street to the stairwell).
In any case, I agree that the removal of locks is something that requires approval at a general meeting. The fundamental security – and by that I also mean physical safety – of the building has been altered and all owners were entitled to discuss it and decide what they wanted to do.
Having people sleeping in stairwells reduces the ability of everyone to get out of a building quickly and safely. And, of course, none of this really matters … until it does. And then it’s a matter of life and death.