By global average, under 15% of farm revenue is derived from government subsidies. USA is below that, at about 10%. Not sure if I'd call that massive, but that's semantics so it's a little hard to argue against. Does potato agriculture get massive subsidies?
> If all subsidies were removed - in order to avoid the influence of moralising politicians - people would eat a lot more potatoes, and a lot less beef.
The assumptions being that 1. potato farming get relatively much less subsidies as beef (and other meat) farming; 2. cost is such a factor in consumption that price change would cause "a lot" of difference. I don't think either are very safe, and as a general statement it doesn't follow that just reducing agricultural subsidies increases ratio of beef to potato (or meat to vegetable): EU subsidies are much higher than US, but USA eats far more beef per capita.
Subsidies go mostly to corn and soybeans. Think those are multipurpose but corn is used to feed livestock, of course. 10 or 15% may be a lot in a low-margin industry, and I don't know how it's split among crops.
No all subsidies are direct. For example, water costs too little in Arizona so foreign companies grow feed stock there to ship home.
If your farm is the recipient of a 15% subsidy, and your margin is only 10%, then the subsidy disappearing means you cannot continue producing the same stock going forward, as you'll be making a 5% loss.
If all subsidies were removed - in order to avoid the influence of moralising politicians - people would eat a lot more potatoes, and a lot less beef.