It also helps that Space Marines are effectively mythical figures to most of the Imperium. Lore generally states that there are only a few million Space Marines running around the galaxy at any given point. Which sounds like a lot, until you consider the fact that the Imperium has, by most estimates, roughly four quadrillion citizens. Against that number, the odds of your average hive dweller or Imperial Guardsman ever encountering a Space Marine are pretty small. A lot of feral and feudal worlds regard them as actual angels of the Emperor and worship them, and not all the chapters discourage this.
I like that aspect too. You've got the few bro-tier chapters like the Salamanders and the Lamenters, who will happily put their butts on the line for ordinary civilians, and then you've got chapters like the Ultramarines and Imperial Fists and a lot of others, who regard baseline humans as inherently inferior but still worthy of polite treatment. Below that are chapters like the Iron Hands, Flesh Tearers, and the Carcharodons, who tell the squishy normals "stay out of our way and you might not get a chainsword up your arse." Then there are the real dickwads like the Angels Excelsis, the Minotaurs, and the Marines Malevolent, who think baseline humans are garbage and treat them as expendable resources.
