The estate tax helps the large farmers get the small farmers land for dirt cheap under the guise of protecting the food supply... the law needs to go.
Farms have had generous exemptions built into the estate tax law for a long time.
Small farms aren't sold off to large farmers the way you describe because of the estate tax. They're sold off in those cases because the estate tax exemption requires the farm to continue operating as a family-owned enterprise -- and many second-generation farm families are unwilling to do that.