Groups like Human Rights Watch have been reporting on problems related to gangs for years. Just a sampling: https://www.hrw.org/publications?country%5B0%5D=9518

I think there's a good argument to be made that "gangs" are a frequent reflection of bad government policies, whether they come from Left or Right governments. Drug prohibitions, lack of rule of law, lack of opportunities for business creation, lack of rights of self-defense, etc... Poverty in general, all of these things contribute.

There's not some simple "liberal gotcha" here.