First, the Brahmajala Sutta is one of the greatest Suttas in Pali Canon. It was the foot print of Gautama Buddha's wisdom. Any possible mis-believes covered in this sutta. It is almost impossible another living being that can articulate this kind of Suttas. The section "Mahāsīla" was intended for the Buddhist monks who are trying to attain Nirvana and the part you are referring in section is concordant with Right Livelihood in Noble Eightfold Path. So it should be part of Buddhist cultures, it should be the Buddha's teaching that monks need to follow, it should be the Buddhists need to cherish the monks who follow this path. It is clearly seen that Right Livelihood make Sanga less tasks and errands where the tasks and errands are adverse to practicing Dhamma to attain the Nirvana. Sanga with Right Livelihood is more respectable and fruitful. You are interpreting it in the right way by agreeing "Mahasila" section in Brahmajala Sutta. Currently, in most countries Buddhists and Buddhist monks are taking Vinaya (the guidances/teachings of Buddha) loosely in general. Buddha said Dhamma will be loosely followed/practiced later and there will be no one like to followed/practiced Buddha's Dhamma and Vinaya eventually. So ignorance to Buddha's Dhamma (Suttas, teachings, practices) is expected. There will be time that the sunset/end of Buddhism in future.
The perspective of Right Livelihood for normal people is quite different from the Buddhist monks who are trying to attain Nirvana. For normal people who are not trying to attain Nirvana, five percepts and not harming to other living being (does not trade in weapons, living beings, meat, alcoholic drink or poison)seems enough for that person not to rebirth as an inferior life (other than human). So it is not appropriate to apply "Mahasila" to normal people and Buddha said "Mahasila" intended to apply Sanga (and person who joins Sanga) many times in Silakkhandha Vagga. Nowadays, with the people of varieties of desires, greeds, thirsts, angers and offenses, it is impractical to apply "Mahasila" in public but instead Buddhist monks should follow since they are maintaining Buddha's teachings.