The size of farms is a topic that I have been discussing with another group. There are some really varied opinions. What constitutes a small farm is not even clear. Most of the world considers anything over 4 or 5 acres a large farm while in North America it is probably more like 100 acres in the east and 1000 acres in parts of the west.
The discussion can branch off to corporate farming versus family farms. Almost everyone seems to agree that family farms are more ideal as it keeps the profits in the community. But unfortunately that is not the way farming is headed. Also corporate farms often are more concerned about profits and somewhat minimize efforts toward sustainability (monocropping, excessive herbicides, poor erosion control, etc.). (From my own observations I have seen that is not always the case, but I have also seen that happen. In general corporate farms place a larger emphasis on meeting a bottom line over sustainability compared to most family farmers).
Larger farms also can be accused of helping to turn the small rural American and Canadian towns into ghost towns.
There is also discussion about the how the continual increasing of yields decrease prices (farmers are victims of their own success). That along with the huge cost of machinery tend to drive farm size up so as to spread huge capital expenses over more acreage. The large machinery then decreases the need for farm labor. For the family farm without unlimited financial backing, the increased financial exposure often leads to bankruptcy on a depressed year. Also family farms, despite their best intentions, often don't have the management skills to actually effectively manage a very large operation. All in all, while migrating to larger farms seem attractive, appropriate and besides they make for really impressive pictures; it may not really be the best way to be going.
In some areas the trend is actually to start downsizing farms. I don't see that as all bad. Things like wheat, rapeseed, corn etc., a larger farm makes sense, but how large? For most vegetables a small 10 acre farm might provide a better answer.