I grow heirloom plants and I try to seed save as much as possible. One summer helped solidify my view on the subject.
A few years ago, the summer was especially wet and overcast. I planted my heirloom tomatoes in early June. I did notice they were about 2 weeks behind the typical growing schedule. The weather continued the same way. I don't go to garden centers or any garden clubs. I started to hear at the supermarket check-outs snippets about tomatoes going bad but thought nothing of it. Finally in July one of my neighbors asked if my tomatoes are dead. I said they are fine. She gave me a strange look like they didn't believe me. I walk my dog regularly and decided to try to find neighbor's tomatoes and look at their condition. All of the tomatoes I saw were covered with a black mold and looked dead. I got on the Internet and found out there was a terrible tomato infestation caused by centrally grown hybrid plants getting infected and spreading the tomato blight disease to the entire area.
Here is a link to learn about the disease:
(Thanks to Cornell Co-Op Extension)
I immediately went out into the yard and inspected the tomatoes. Some had a few symptoms but all were growing and producing fruit. The garden centers destroyed their plants. Local officials were recommending destruction of in-ground tomatoes to destroy the disease. I kept plugging along. I kept physical contact with the plant to a minimum and made sure I watered the soil and not the plant. I stayed away from other tomato plants in general.
The end of year production was down but all of my plants survived. This made me a believer in heirloom plants. They clearly had superior resistance to the tomato blight.