How do taboo acts work in tantra if people don't see the acts as taboo?
Tantric symbolism is always multifaceted. Although a lot of the imagery in Tantra is very taboo, there's more to it than just shock value. For example, the five nectars of urine, feces, menses, semen, and bone marrow aren't visualized in a skull-cup as an offering because they are transgressive, but because they represent the five aggregates, and refering to them as nectar represents that for an enlightened being they are innately pure. Even if someone doesn't find any particular part of Tantra to be taboo, they still would make sense in terms of their other symbolic aspects.