“Festival days, vulgarly called Holy-days, having no warrant in the word of God, are not to be continued.”
And here we see how removing Christianity from the public square began.
Hardly. No one is preventing you as a Christian from interacting as an apologist for Christ in the public square.
The Church, however, has a responsibility before God to keep His worship pure and undefiled. Picking up the worship refuse from other traditions and adorning Christ's Church with them is not the solution.