The question of moderation came up when talking with people on my mission, trying to get them to stop smoking or drinking alcohol. It comes up trying to help people lose weight or develop exercise programs. It comes up when I try to help people understand the principles in For the Strength of Youth, or talk about prayer or scripture study. It comes up when I invite people to Institute or encourage them to attend Church activities or even attend the temple. And, more than anything, it comes up when I bring up the topic of healthy food and exercise, and try to explain that our bodies are temples of God (Would you use inferior materials to build a temple? How about in "moderation" - like, say, 5 out of 100 windows made of cheap plastic instead of imported glass?).
Here's my feelings on "moderation," echoed by Dallin H. Oaks:
"the Savior said that if we are “lukewarm,” he “will spew [us] out of [his] mouth” (Rev. 3:16). Moderation in all things is not a virtue, because it would seem to justify moderation in commitment. That is not moderation, but indifference. That kind of moderation runs counter to the divine commands to serve with all of our “heart, might, mind and strength” (D&C 4:2), to “seek … earnestly the riches of eternity” (D&C 68:31), and to be “valiant in the testimony of Jesus” (D&C 76:79). Moderation is not the answer" (Ensign, Oct 1994).
When the prophets have used moderation to talk about commitment to the gospel, it has always been about letting specific pieces of the gospel eclipse your view of good things - insisting that you have to clean your house, hence you can't go to Church and you don't have time to read your scriptures. It's absurd to say that God wants you to lessen your resolve so that you can live a moderately sinful life, or eat garbage in moderation, or exercise moderation in acting on your carnal urges.
Here's a much better example - Alma 57 (emphasis added):
20 And as the remainder of our army were about to give way before the Lamanites, behold, those two thousand and sixty were firm and undaunted.
21 Yea, and they did obey and observe to perform every word of command with exactness; yea, and even according to their faith it was done unto them
25 And it came to pass that there were two hundred, out of my two thousand and sixty, who had fainted because of the loss of blood; nevertheless, according to the goodness of God, and to our great astonishment, and also the joy of our whole army, there was not one soul of them who did perish; yea, and neither was there one soul among them who had not received many wounds.
26 And now, their preservation was astonishing to our whole army, yea, that they should be spared while there was a thousand of our brethren who were slain. And we do justly ascribe it to the miraculous power of God, because of their exceeding faith in that which they had been taught to believe—that there was a just God, and whosoever did not doubt, that they should be preserved by his marvelous power.
27 Now this was the faith of these of whom I have spoken; they are young, and their minds are firm, and they do put their trust in God continually.