[Either today, or in a world without Malaria, would you suggest releasing a devastating plague in Africa, and go on TV to tell the victims that they were a burden on the world and you had judged their lives to be not worth living, so were reducing the population to a more manageable level?]

Assuming we are not willing or capable to do better (Help them have lives worth living, fix resources and population management issues "directly"...), then yes. Not a devastating plague + broadcast though. A sterilization plague that ideally targets the less intelligent 90% or whatever. Done in secret and presented as a natural occurrence, paired with compassionate material and "bureaucratic" assistance.

I don't think it's impossible to judge a life as not worth living. Survival instinct is not rational.