Many, __________, hesitate to publicly broach such question for fear of nurturing discrimination.

'Understandably' is the appropriate discourse marker here, meaning 'for reasons that are easy to understand'. It conveys that the speaker sympathises with the hesitation of many people to broach such topics due to fear of fostering discrimination. 'Despite' is a preposition requiring an object, 'until' is a time conjunction, and 'of course' indicates certainty — none fit the sympathetic explanation context as well as 'understandably'.