I used to think it would be bad if they ever removed deployable ladders from siege, but after it was done I actually preferred it more.
As has already been said umpteen times, defense has more of a chance of winning, although attackers still have the advantage on most maps.
Another disadvantage of having deployable ladders is that defense doesn't actually get to use any creativity or coordination - it's just 'camp the flag' every map. Without the ladders defense actually gets to enjoy using the rest of the map and defend some walls, ramps, doors, etc.
The ONLY way deployable ladders should be let back in would be if attacker spawn was reduced by at least 10 seconds. Otherwise there's just no chance 9 times outta 10.