"Since these medications are not regulated for use in humans, there are no guarantees as to their quality or potency."
Also no regulation as to how they are used. Super-bugs are being bred by over-use, and a careless or ignorant individual can make his/her own infection hard to kill by using antibiotics in other than the approved way (e.g. not finishing the course).
It's not just that. Not all anti-biotics are suitable for all infections - treating a skin infection and a gut infection will tend to require different anti-biotics.
Self medication is possible and, with enough research, can be done successfully and responsibly, but for most people it's really not a good idea.
Also no regulation as to how they are used. Super-bugs are being bred by over-use, and a careless or ignorant individual can make his/her own infection hard to kill by using antibiotics in other than the approved way (e.g. not finishing the course).