这句话的主干是Many(主语) argue(谓语) that the costs are too high(宾语从句) and(连词) that differences need to be maintained(宾语从句).
在宾语从句the costs are too high中,costs是主语,are是谓语,high是表语；在宾语从句differences need to be maintained中,differences是主语,need to be maintained是谓语.
before we quickly and completely lose all sense of who we are,where we came from and what choices are still available to us是介词结构作状语,修饰动词结构need to be maintained.在这个介词结构中,we是主语,lose是谓语,sense是宾语,of who we are,where we came from and what choices are still available to us是介词结构作sense的定语.
在who we are,where we came from and what choices are still available to us中,两个are都是现在情况,而came却是已经发生了的情况,即我们的到来是过去发生的事.
——【译苦思甜】团队成员荣誉回答