Of course we should warn overeaters, it's self indulgence seeking fullfillment in food, as in all worldly endulgences keeps us from the true fullfillment, which is the love of God in our hearts.
An overeater needs help as much as a masturbator, and i have struggled with this sin and would find it no use people not condemning it, people should help another who sins out of love, not looking down on them, but being a servant to them of Gods love.
I want my brother to rebuke me, i want to be warned of sin, i want to know sin to avoid it and be helped to overcome it.
I see an excuse for nearly every sin today, and even if it is recognized as sin, they then seems to be a sort of encouragement in it, by saying we love you as you are, forgetting the love of Christ was to free us from sin, He died for our sins, not for us to still be servants of them but free from the bondage they kept us in.
We still love another when they are sinners, for Christ died for us when we were yet sinners, but it wasn't for us to remain such, otherwise His death was in vain.
We also out of love for sinners and our brethren want them to overcome sin, this is love not some evil as the world calls it today.
Lev 19:17 Thou shalt not hate thy brother in thine heart: thou shalt in any wise rebuke thy neighbour, and not suffer sin upon him.
1Ti 5:20 Them that sin rebuke before all, that others also may fear.
2Ti 4:2 Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all longsuffering and doctrine.
2Ti 4:3 For the time will come when they will not endure sound doctrine; but after their own lusts shall they heap to themselves teachers, having itching ears;
2Ti 4:4 And they shall turn away [their] ears from the truth, and shall be turned unto fables.