Final answer:
Monastic discipline, with its strict rules and lifestyle, is the aspect of Buddhism considered less embraced in the Western world, in contrast to meditation practices and reincarnation beliefs.
Step-by-step explanation:
An aspect of Buddhism that is considered less popular in the Western world would most likely be D. Monastic discipline. While meditation practices and reincarnation beliefs have gained a certain level of familiarity and acceptance in the West, the strict lifestyle and rules governing monastic life are not as commonly embraced in Western culture.
Monastic discipline requires a level of commitment to living in accordance with a set of precepts that include celibacy, poverty, and obedience, often within a monastic community, which are practices that contrast with the values of individualism and material success prevalent in the Western world.