One certainly can. But the original question was whether it is "stupid" to get them in pairs. The answer is no.
Doug, If you are going to get a number of KB's, I would really suggest two pairs. While you can to probably 80% of the possible exercises with just one, you can get that extra 20% with pairs and have alot of fun. If you are on a tight budget, how about 2x 35# and1 x 53#. THis way you can still get up to your 70# swinging weight... (now I re-read your original post and I just suggested exactly what you originally were going to do...)