Final answer:
The environmentalist's speech focused on the advantages of lab-grown meat, its potential benefits for the environment and health, and the economic and cultural challenges associated with reducing traditional meat consumption.
Step-by-step explanation:
The main topic of the environmentalist's speech was about the advantages of lab-grown meat. While the audience may not have seemed receptive, the environmentalist was likely discussing how synthetic meat alternatives could alleviate the environmental impacts associated with traditional animal farming, improve health outcomes associated with a plant-based diet, and potentially reduce costs for consumers in the long-term. This is in light of research suggesting that despite the environmental and health benefits, many consumers find it challenging to shift away from meat consumption due to taste preferences, cultural importance, and the belief in meat's role in a healthy diet. Moreover, this transition raises concerns about the economic impact on farmers and the efficiency of nutrient delivery from lands not suitable for crop production to feed a growing human population.