If the DEA started arresting patients, I'm sure there would be such a political backlash that serious movements to take marijuana off the schedule 1 list would become real. Even if they did go after patients, they don't have the resources to charge every single one, and even if they did, any judge that wants to be voted in again would dismiss any case regarding a medical marijuana patient.

So you shouldn't be that paranoid, but I understand your concern. Besides, growing your own is WAY cheaper than going to a co-op, I'm not sure if you are familiar with the prices, but I've become accustom to spending $60 for an 8th. If you are a heavy user this can be extremely expensive. However, many co-ops do offer clones for growers if you are interested.

Oh, and for background checks, being a medical marijuana user DOES NOT show up. That's just to check your criminal record such as any records of being arrested, getting a DUI, etc.