Many people won't understand why it was necessary for the government to cooperate with the mafia in order to suppress labor unrest. However, a government must do everything possible to stay in power. If the entire country shut down because of a labor strike, there wouldn't be a country to govern, so the government just did what it had to.
Labor unions can be champions of the people or detriments to the economy, depending on their incarnation, but they are fundamentally allowed within the US. The US government using the mafia to control labor in some way is as if a dictatorship uses state militias to do the same - something that should be avoided at all costs.