Wine is prescribed because the expression "the fruit of the vine" is part of a traditional Jewish thanksgiving formula from that era. Lightfoot explained this, and I don't think any historians have reason to doubt it. Not only is the Lord's Supper a sacrament—it is also part of public worship, and therefore comes under the Regulative Principle. We are not at liberty to change what the Lord has prescribed as a sacrament and as a vital part of public worship.

Because of their connection to public worship, sacramental bread and wine are (the only) prescribed symbols of the church. Even the ubiquitous cross doesn't have the same status.

I think that whether the wine should be red or white is best determined by documented Jewish practice from the era, although I am partial to red because of the symbolism (Revelation 14 and 19 seem to indicate red wine). I'm not a historian, so I cannot provide any more information regarding this.

The argument that grape juice may be used to accommodate weaker brethren or former alcoholics is flimsy. Did the Lord, who knows all and decrees all that comes to pass, not know that these weaker brethren would be stumbled by the use of sacramental wine? Are we wiser or more compassionate than God?

The Belgic and Westminster Confession prescribe sacramental wine. Churches that subscribe to these subsidiary standards ought to practice what is prescribed in their confession.

If a former alcoholic has scruples about sacramental wine, he should abstain and wait for the wedding supper of the Lamb, where we will be able to partake of the celebration with real wine.

In this was manifested the love of God toward us, because that God sent his only begotten Son into the world, that we might live through him.