In a secular country, we must be open to varied ideas and positions. However, we ought to insist that the other side should reciprocate the same when we disagree with them. Because, very often, especially in the west, the Christian position is ignored or jeered at.
Must we engage? I think we must engage with the moral positions of others without condemning them. While I think it is important to communicate the reasonableness of the Christian position our moral posture in these arguments must be clothed in grace and love.
How do we engage? Natural Moral Law argues for the Christian position appealing to reason without referring to the Bible yet upholding the biblical position. Being familiar with those arguments will come in handy. Many of C.S. Lewis’ books are a good start.
Why are we engaging? We must also be able to gently point out the logical outcomes of their choices and the chaos and meaninglessness that might ensue. And as an alternative creatively offer Jesus as Logos - the one who can bring order and meaning into their lives.
All the best as you engage with your circle of influence.