Good Friday has an ancient pedigree in the early church (as least back to the 2nd century and thus far more ancient than Christmas) and due to its association with Passover we can date it more or less accurately. Furthermore, due to its connection with Christ's resurrection it has ties to the Lord's Day, and thus we have a prima facie justification for its inclusion in our calendar.
However, we still would have to establish that God wants it as part of his calendar, not to mention that in this there is a tacit assumption that the church's calendar is concurrent with his. At best we might say that it is a convenient time to remember the suffering and death of Christ but we already have that in the Lord's Supper. Are we to say that is not sufficient? Indeed, what he has commanded is sufficient (Matthew 28:19-20).
And we must remember that separation or distinction (of days) establishes them for holy use. That is at the very heart of what a biblical definition of holiness entails. Consider, after all, the real holy days of old. They were appointed by God for his people and then ceased to be of obligation when Christ came. God was the maker and unmaker. They were tolerated as long as the church was primarily Jewish in number (origin), but they were also condemned by the apostle Paul when they being used in a superstitious way (Galatians 4:9-11). Now if that was true of what God ordained, how much more is it true of what he has not?
I know that people will say it is not a holy day but it is treated by much of Christendom as such (and even by the world besides). You may say that has nothing to do with us but how can you separate yourselves from such? It is all embedded in the very day: in its past and present celebration because of the manner in which it was initially imposed. As Mr. Coldwell has noted, it is a monument of idolatry and will never be anything else, all honourable intentions aside.
Moreover, if we are truly not obligated to the day then it is of no account. And then why call it Good Friday or, the following, Resurrection Sunday? Why say that Jesus rose on this particular Lord's Day when we will not say it every Lord's Day? Or say it with more emphasis today when objectively nothing about this Lord's Day lends itself to that statement? Why attribute something to it that God does not? Which is to say, why make high places when God has not appointed such. If it to be replied that God appointed sacrifices so we may do so as we please (or as our collective wisdom may grant), we must reckon with the fact that God also told his people, how, where, when, by whom and why. And if we are to say that Good Friday has nothing to do with those corruptions of old anymore than the Lord's Supper has to do with the Mass, we might simply reply that at least the Lord's Supper was established by Christ.
From my youth we had a simple Good Friday service but even that has been corrupted into a thing far more superstitious than even the Dort fathers intended. Indeed I know of otherwise godly people who think more highly of these days than they ought. If I can speak this way, the "common man" thinks that way; how can he not? His pastor affirms him in his conviction when he treats the day as anything other than one for common use. The men of old who prescribed the celebration of the church calendar in the Netherlands sought to accommodate or grandfather in practices that had already returned into our pure churches, practices which by then had been foisted on the church by the magistrate. That was an Erastian error indeed but now we double down on lifting up the authority, desire or whim of the body over the head.
I am amazed that otherwise solid churches now celebrate Lent, Ash Wednesday and such customs inherited from the days of the church's corruption by Antichrist. I see vestments, colors, candles, furniture and all manner of cyclical nonsense intruding into the worship of God. Even Reformed churches now practice such things and why? Tell me where that came from and you instruct yourselves what more of false worship of which you have to rid the church. Dare we admit that our form of prelacy is the road to papacy? I truly hope that this narcotic is not a gateway to the bridge for more to cross the Tiber.