I'm not sure I agree.
For a start, it's a fairly niche case that you would have to sell an entire farm to pay an IHT bill. By the time you get into the bills being really significant, it's almost certainly because you have a lot of land, and would only need to sell a small amount to pay the IHT. I still think we're being asked to conflate two contradictory 'farmers', the ones who earn no money are almost certainly not the ones who will have huge IHT bills.
Losing their livelihood is also a bit of a red herring. If they absolutely had to sell, then they'd be potentially be losing a business they care about, but surely they'd then be a very wealthy person? If we're being asked to accept that hugely valuable farms make almost no money, then they'd be a lot better off financially selling up.
Losing a longstanding family business may be tough, but if you come out of it as a multi-millionaire, who can retire the next day, then that's a better position than most of the country are in.