We weren't given, e.g., the Great Commission for no reason--and fulfilling the Great Commission requires
tikun-ha'olam. If you live your life by that "'Expectation is the root of all heartache'," so much for being a Christian, then. Jesus told us to expect pain & sorrow, and that things will get better if we try to help them be. After all, " “You are the light of the world. A city that is set on a hill cannot be hidden. Nor do they light a lamp and put it under a basket, but on a lampstand, and it gives light to all who are in the house. Let your light so shine before men, that they may see your good works and glorify your Father in heaven."
And what does a light do? Well, "there is nothing hidden which will not be revealed, nor has anything been kept secret but that it should come to light." Lights shine on things. Lights reveal things. Lights also, if they can, refine things. Remember that lights contain heating elements. "Many shall be purified, made white, and refined, but the wicked shall do wickedly; and none of the wicked shall understand, but the wise shall understand."
You don't help people by keeping things in the dark, let alone by not using things to learn from them. After all, "[a]s iron sharpens iron, [s]o a man sharpens the countenance of his friend." Not only that, but light needs to be a light to darkness as well, that the darkness may come into the light if it can.
For example, "if the whole church comes together in one place, and all speak with tongues, and there come in those who are uninformed or unbelievers, will they not say that you are out of your mind? But if all prophesy, and an unbeliever or an uninformed person comes in, he is convinced by all, he is convicted by all. And thus the secrets of his heart are revealed; and so, falling down on his face, he will worship God and report that God is truly among you."
People are not going to be convinced if the Church seems out of touch with realities of the world. Focusing on "sweetness and light" and the "positive" all of the time is not being in touch with what's going on. Granted that you are to "[s]et your mind on things above, not on things on the earth. For you died, and your life is hidden with Christ in God." That doesn't mean to ignore or mitigate the realities of the world--in fact, that means that you're to "not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God."
Remember that the world tries to hide things, keep secrets, make things look better than they are. No wonder, then, that the world won't help the least of these. After all, why would one help the least of these if he or she denies or mitigates them or their circumstances in the first place?
"“Then He will also say to those on the left hand, ‘Depart from Me, you cursed, into the everlasting fire prepared for the devil and his angels: for I was hungry and you gave Me no food; I was thirsty and you gave Me no drink; I was a stranger and you did not take Me in, naked and you did not clothe Me, sick and in prison and you did not visit Me.’
"“Then they also will answer Him, saying, ‘Lord, when did we see You hungry or thirsty or a stranger or naked or sick or in prison, and did not minister to You?’ Then He will answer them, saying, ‘Assuredly, I say to you, inasmuch as you did not do it to one of the least of these, you did not do it to Me.’ And these will go away into everlasting punishment, but the righteous into eternal life.”"
After all, "[p]ure and undefiled religion before God and the Father is this: to visit orphans and widows in their trouble, and to keep oneself unspotted from the world." "To keep oneself unspotted from the world" surely does not mean to focus on the "positive" and "sweetness and light" all of the time when the "positive" and "sweetness and light" is surely not what widows and orphans are going through. Besides, again, how will you "make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit," if you won't address the reasons why they need the Father, the Son, and the Holy Spirit in the first place? After all, there's no need--because there's no lack or void--of the Father, the Son, and the Holy Spirit in a "positive" world of "sweetness and light".
Furthermore, we're not in that "positive" world of "sweetness and light" yet. In that day, "[n]o more shall every man teach his neighbor, and every man his brother, saying, ‘Know the Lord,’ for they all shall know Me, from the least of them to the greatest of them, says the Lord." But it's not that day yet--so we need to live in the reality of the day that we are in right now--and living in the present requires that we focus on and try to make better the reality of the present, no matter how un-"positive" and lacking in "sweetness and light" it is.