Answer: Opposing side
Step-by-step explanation:
Substitutes to the products offered by monopolies are frowned upon by monopolies because it means that they cannot raise prices whenever they want anymore because people could simply switch to the substitutes.
Substitutes therefore reduce the power of monopolies. Marijuana is a substitute to beer as a recreational product so beer companies would be opposed to it being legalized as it would pose a threat to whatever dominance they have in the recreational sector.