Does the vacuum of space generally require a closed system? And venting the CO2 is bad for the same reason that the heat death of the universe is bad; at some point you have converted all of the usable stuff into useless stuff and have vented it somewhere that you will be unlikely or impossible to be able to recover it.
If we do that, we will have to resupply the O2 in some way other than converting CO2 back to oxygen. Either shipping new gas to the moonbase, or having the moonbase convert organic material on the moon to O2 (which sounds a lot more expensive and difficult than having plants scrub CO2 into O2 for us).
This is also not to mention the other valuable things were venting with the CO2 (heat for one; I assume keeping a moonbase at a livable temperature would be a struggle). Your scrubber also has to be able to replenish the gas while it's venting, or you risk having rapidly fluctuating pressures in the moonbase. Which is going to be uncomfortable for living things, and will require whatever the moonbase is made out of to be able to handle those changes in pressure (again, I imagine having pressure that fluctuates like a bounce house with a group of sugared up children in it is less than ideal). It's not hard to imagine a non-rigid structure like the base from The Martian bouncing off the surface of the moon when it rapidly constricts from venting CO2 and then rapidly inflates as the O2 replenisher kicks on. It would become a massive bouncy ball in 0G.
If we do that, we will have to resupply the O2 in some way other than converting CO2 back to oxygen. Either shipping new gas to the moonbase, or having the moonbase convert organic material on the moon to O2 (which sounds a lot more expensive and difficult than having plants scrub CO2 into O2 for us).
This is also not to mention the other valuable things were venting with the CO2 (heat for one; I assume keeping a moonbase at a livable temperature would be a struggle). Your scrubber also has to be able to replenish the gas while it's venting, or you risk having rapidly fluctuating pressures in the moonbase. Which is going to be uncomfortable for living things, and will require whatever the moonbase is made out of to be able to handle those changes in pressure (again, I imagine having pressure that fluctuates like a bounce house with a group of sugared up children in it is less than ideal). It's not hard to imagine a non-rigid structure like the base from The Martian bouncing off the surface of the moon when it rapidly constricts from venting CO2 and then rapidly inflates as the O2 replenisher kicks on. It would become a massive bouncy ball in 0G.