His socialist policies. Rent control, land reform, social security, and so on. Later the Shah followed and expanded the same social policies. And that is what tore the fabric of Iranian society and brought us the 1979 revolution. There is evidence that Mossadegh did part of this to counter the great influence of the Toudeh party but nevertheless he followed the footsteps of the dominant portion of Iranian roshanfekr class, past and present, and that is to at best emulate Europe's socialist ways, thinking this must be nirvana. It could not be further from the truth, the reality. It is what has proven to bring Europe to its knees. It is what nearly bankrupted the once great United Kingdom. And Iran is most certainly not Europe. European societies are extremely uniform compared to Iran so that the tyranny of socialism is more moderate in Europe than it would be in Iran.
Consider for example land reform. Iran had a well established arbab rayat system. This is not ideal, nevertheless Iran had a great surplus of farming. Mossadegh first in a limited way and the Shah next in a total way aboloshed Arbab ra'yat. What was the result? A decimated farming sector with greatly, greatly reduced production AND the 1979 Revolution. This is how it worked. When the Arbab lands were divided and given to the peasant farmers, the newly independent land owners prove to have zero interest in owning the land and growing production. Instead the great majority sold the land, had chelokabob and moved to the cities with the money. Once the money ran out they only developed greater and greater oghde and disdain for the Shah and Iran's educated middle class. Nearly all of the obash among the revolutionaries and now the obash in charge are these type of people or the sons and daughter of these type of people.
There is a much better way.