The problem with unlocking the forge on day 1 is that it is a stage-defining piece of technology. You basically have the stone-age before you unlock it (stone axe, stone shovel, wooden club. That kind of technology). After unlocking the forge you have access to hammers, axes, shovels, pickaxes, iron traps, buckets and the like. You've entered the iron age, so to speak. So by being able to build a forge on day one you completely bypass the early game. This drastically reduces the value of these tools, since you can get them on day 1-2 already.