I think one of the ways the social gospel has influenced the modern church is in the idea that we are all one people, and as one people, we should all support one another, regardless of religion and creed. This, of course, is not a biblical concept. Instead, what we see is the command for Christians to support government in terms of taxes (the government sets apart what belongs to it from your wages, and they do not belong to you or Christ as a part of His kingdom at that point) and the church in terms of everything else.
The reason why this is the case is due to the fact that to support someone with the resources of Christ is to support their ministry. And everyone has a ministry, believer or unbeliever. I think most people miss this in Scripture, but there are a few commands that we are not to support the lifestyles and proclamation of false gods, false worldviews, false theology, and evil ethics.
This is why Timothy is told to not support widows, who may be in need, but are living lifestyles that communicate evil to others (1 Tim 5:9-15). In fact, Paul argues, with what I think is a reference to giving blessings of the kingdom to someone, that to give someone who is doing evil those blessings is to partake in their evil deeds (v, 22).
Instead, Paul commands that widows who have a good witness of good works and faithfulness to Christ are to be supported, along with elders who are faithfully doing the good work they are called to do.
Likewise, John tells believers to not even greet anyone with a false teaching because the person who gives him even a greeting "shares in his evil deeds" (2 John 10-11).
"If anyone comes to you and does not bring this teaching, do not receive him into your house and do not give him any greeting, because the person who gives him a greeting shares in his evil deeds."
Instead, John urges believers to support other believers in ministry instead.
"Dear friend, you demonstrate faithfulness by whatever you do for the brothers (even though they are strangers). They have testified to your love before the church. You will do well to send them on their way in a manner worthy of God. For they have gone forth on behalf of “The Name,” accepting nothing from the pagans. Therefore we ought to support such people, so that we become coworkers in cooperation with the truth." (3 John 5-8)
Is John merely arguing that such men should be supported but everyone should be supported as well, or is he arguing that really only faithful brothers should be supported? I think, in light of what he says elsewhere, he is arguing that only the latter should be supported.
One does not hear these ideas anymore in the church today though. We are bombarded with songs, sermons, and books, along with a general "feel good" spirit about secular society and the oneness of humanity that largely ignores these texts.
But if I am to give support to everyone, why would these texts tell me not to do so? Why would they say, instead, to give support to those who are faithful to Christ? Why no commands to give to my fellow man regardless of whether he spews out theology and ethics that are hateful to God?
Paul says that all men, apart from Christ, are murderers. Our instrument of murder is our communication of false gods, theology/worldviews, and the evil deeds that one does. It is our ministry of death to the world. As such, the apostles did not see supporting ministries of death, and argue that to do so is to partake in those ministries.
This is the flip side of partaking in one's good ministry by supporting it. Not all Christians could go on Paul's missionary trips, but they could partake of those deeds to support him; and in doing so, his deeds became theirs. Likewise, not all Christians may have had a hand in the good testimony that a particular individual who is faithful to Christ might have, but they do have a hand in it when they support such a one.
On the reverse though, a person who is not faithful to Christ has a ministry too, and because of this the apostles warn people that it is possible to partake in another person's evil deeds by somehow supporting that person.
It is for this same reason that Christians don't argue that we should send money to the poor people in ISIS. Have you heard anyone arguing that? If we should give to all of the poor, regardless of their theology and deeds, why not to poor members of terrorist groups? We don't do it because we make the connection there that we would be supporting what they believe and are doing. Likewise, we don't support poor Mormon missionaries because we don't want to partake in their work. The problem with the modern Christian is that he doesn't realize that everyone has a ministry, and there are good ministries that should be supported, and there are evil ministries that should not be.
Hence, the New Testament does not ever argue that we should give either to the unbeliever or the unfaithful Christian because it does support the ministries of evil. Instead, it calls people out of those ministries to faithfulness to Jesus Christ as Lord. But in the New Testament view, there is more than one way to participate in the evil deeds of darkness.
Let nobody deceive you with empty words, for because of these things God’s wrath comes on the sons of disobedience. Therefore do not be partakers with them, for you were at one time darkness, but now you are light in the Lord. Walk as children of the light –for the fruit of the light consists in all goodness, righteousness, and truth – trying to learn what is pleasing to the Lord. Do not participate in the unfruitful deeds of darkness, but rather expose them. For the things they do in secret are shameful even to mention. But all things being exposed by the light are made evident. (Eph 5:6-13)