We are told to rebuke with all longsuffering and doctrine (See: 2 Timothy 4:2). Not sure what you think that verse means.
Anyways, I believe the sugar discussion is a diversion away from the evil that happens from alcohol. Sure, sugar is bad, but it is not as bad as alcohol in my view because alcohol clearly destroys lives in numerous ways even without death. Families can be ruined and can be involved in other crimes because of alcohol. For alcohol destroys good judgment. Things people normally would not do while sober, they would do while under the influence of alcohol. I really should not have to educate folks on this basic truth. See, back in my day, when I grew up, my school showed me the horrific videos of all the car crashes and problems that took place as a result of alcohol. Maybe your school did not play these videos. I don't know. But what I do know is that while sugar can hurt lives, it is a slow killer, and it is not like alcohol that can kill a person in one day.
As for mixing water with wine: Yes, I agree that the early church did that for medical reasons, but not for social reasons. I believe the Israelite drank wine mixed with several parts of water, but when Jesus came, He made new changes. How can I prove it? Well, the New Testament commands tell us to be sober minded many times (
1 Peter 1:13 KJV) (
1 Peter 4:7 KJV) (
1 Timothy 3:2 KJV) (
1 Timothy 3:11 KJV) (
Titus 1:8 KJV) (
Titus 2:2 KJV) (
Titus 2:4 KJV) (
Titus 2:6 KJV) (
Titus 2:12 KJV) (
1 Thessalonians 5:6, 7, 8). For God's Word wants us to be sober minded for our adversary the devil, is a roaring lion, who walks about, seeking those whom he may devour (
1 Peter 5:8 KJV). If this is the case, then the moment a person takes a sip of even watered down wine, they are less sober minded then they were before they drank. If one does not care to obey the New Covenant, then by all means, they can do as they please and serve themselves instead of their Lord. I prefer to follow the words of Jesus, and the words of His followers, and not those who are seeking to defend a drink.
“For the kingdom of God is not meat and drink; but righteousness, and peace, and joy in the Holy Ghost.” (Romans 14:17).