The HLF is most commonly portrayed as an organization of radical vigilantes, known throughout the general TCB universe as a terrorist group that stands for one goal: the survival of humanity at any cost, as well as the liberation of their homes and freedoms. Their methods are usually seen as extremist and brutal. They absolutely refuse to tolerate anyone who helps or supports Celestia or Equestria.
The HLF originated in Blaze's story, being little more than thugs who believe that all ponies must be eliminated to protect humanity. They've been a staple of Conversion Bureau stories ever since.
The depiction of the HLF varies from story to story. In some stories, they're little more than thugs on the level of violent street gangs and considered a nuisance; in other stories, they can be highly sophisticated paramilitary organizations with enough firepower and resources to rival the army of a small country. Additionally, the roots of their opposing stance towards ponies can stem from a multitude of causes. Such reasons can run the gamut from them simply being religious extremists who see ponies as an affront against nature, to their hatred being born out of desperation and necessity.
"Straight" TCB stories depict them as the villains and a danger to ponies and the humans that wish to join the Equestrians, akin to terrorists. Anti-TCB stories (such as Ten Rounds) often have them as heroic partisans fighting against the genocidal campaign of the Equestrians. However, notable anti-TCB story The Other Side of the Spectrum has the HLF in a mixed role - though they will valiantly fight against the PER and the newfoals, they are also rigidly anti-pony to the point that even human sympathizing ponies aren't safe from their wrath.
Regardless of depiction, the HLF is still considered highly dangerous, often having access to military equipment and homemade weapons, including bombs, cannons and pipe-guns.