Why did social reform and social control often intermingle in the Progressive Era? Can such objectives be separate?
The Progressive Movement of the early 20th century first sought to 'reform the ills of society' created by industrialization but the movement continues till this day in the U.S. Regardless of the type of social reform it was and is generally born at the 'grassroots' of American society with many ideas taking shape at the kitchen table. However, progressives believed that without government legislation and regulation their social reform policies would have little chance of actually changing society. Therefore it could be argued that with social reform comes a certain degree of control by the government mandating that the social changes in the form of law be obeyed by the people, thus social control within the society.
Many Progressivist thinkers saw the call for social reform as demanding more control for those who had been kept silent in the American Discourse. I do not think that this demand was exactly similar to what the term "social control" would end up indicating, but it was there. Progressive reformers and their reforms sought to grab control of a political and economic order that did not value many of the citizens involved in it. Workers who had no rights, citizens who had not voice, and individuals who were atomized from their own sense of being in the world were the primary rallying points for the Progressive social reformer. With this in mind, there was a desire to take control of the situation and inject these new voices into the dialogue in order to become part of the American discourse of power.
In my opinion, social reform and social control often came together because the reformers (mostly middle class "natives") wanted to change the behaviors of people who did not always want their behavior changed. This meant that the reform would have to be forced on people -- this means social control is necessary.
A perfect example of this is Prohibition. The reformers wanted to stop people from drinking, but the people did not want to stop -- they did not think what they were doing was wrong. So control was necessary.
I do think that much social reform is possible without social control. For example, prostitution is something that social reformers would like to eradicate. I doubt that many prostitutes would choose to be prostitutes if they had a clear choice and so they would be less likely to need to be controlled in order for reform to occur.
As I reread your question, I think maybe I have used "social control" in a way other than what you mean. So let me give an alternative answer.
The reformers were a middle class group who wanted to control those that they thought were beneath them and possibly dangerous. They thought that immigrants, for example, needed to be controlled lest they harm American society. This is why they were at least as interested in controlling immigrants as in helping them.
Prohibition is a good example again. A major goal was to control workers better so that that they would be more efficient at their jobs. This was a goal the middle class supported.
I think it can be very hard to determine what objectives reformers truly have. For example, when people try to prevent drug addiction, are they trying to help the people who are or might be addicted? Or are they trying to control populations who might harm the reformers' interests (by stealing from them, for example)? It's sort of a matter of how cynical you are, I think.