If this is the case with direct statements and commands, however, it is certainly the case with what is inferred and applied. The problem, of course, is that the Lord makes it clear in the Sermon on the Mount that what is to be inferred by direct statements and commands is as equally binding as that which is directly spoken.
Hence, a command to not commit adultery means that you don't have anything to do with the sphere of what is considered adulterous thinking and all of its applications. To not commit murder means you don't have anything to do with the sphere of murderous thinking and all of its applications. The person who may refrain from literally carrying out what is prohibited by the direct command, but is guilty of this type of thinking and one of its applications in life (e.g., attacking a brother verbally due to hatred) is just as guilty to be sent to hell as the person who went out and murdered him. Christ, of course, is not saying that these are the same actions, but that they are the same types of sins, and therefore, they are equally as damning.
What this means is that one cannot get away with saying, "Well, the Bible doesn't technically say that such and such is wrong and such and such is right; and therefore I am not bound to it," or "Well, that is just your inference and application of the subject, but I am only bound to what is explicitly commanded." If Christ condemns the Pharisees for not honoring their parents because they do not do so financially, even though the command was never so specific as to apply to financial means, then what pleases and displeases God has more to do with inferences and applications than most Christians make out. (Remember, the Pharisees aren't the original audience of those commands and are in a completely different situation in life than the original recipients, and yet, God still expects them to obey and apply it to every sphere in life.)
This is important for when we study the Bible, since much of the Bible is communicated in a variety of genres, a major one being narrative. If we are equally bound to what is inferred and all of its applications, then the teachings of narrative are also as equally binding. Hence, when the Deuteronomistic History communicates things like refraining from graven images of God, the inclusion of gentiles who give their allegiance to YHWH into Israel and the exclusion of Israelites who break allegiance with him as non-Israel, the centrality of worship and the presence of God through His Word, etc. are all equally binding concepts upon our modern thought and practice. In other words, these are not merely for Israel. This is not just a story to tell us what happened in the past. In fact, it's not even primarily that. Instead, it's main purpose is to communicate via inference principles and ideas that we are meant to believe and apply.
As Vern Poythress states,
In addition, we may say something about the application of God's words. God expects his words to be applied in many situations throughout history. He binds us to obey, not only what he says in the most direct way ("meaning"), but what he implies ("application"). Each valid application is something that God intended from the beginning, and as such has his sanction. Divine authority attaches not only to what he says most directly, but to what he implies. It attaches to the applications. ("Divine Meaning of Scripture")
If this is true, then when we approach a text like Genesis and see the creation ethic that it teaches via inference, that creation ethic is as binding as any directly given divine command might be. The inferences are not merely descriptive of ancient Israelite beliefs and practices. The descriptive information is what sets up the narrative and clothes it, but the teaching itself is what is inferred as true given the literary presentation of the text. As such literature set in narrative often makes arguments implicitly rather than explicitly, and if God therefore chooses to use narrative as a genre, then what He is teaching us to believe and obey must be drawn out via inference.
Hence, if Genesis teaches via inference a creation ethic that condemns whatever undermines the procreation and preservation of human life then condemnations of practices that are contrary to that ethic carry as much authority as direct and explicit commands to us. What this means is that Christians don't need an explicit command against things like homosexuality, contraception, abortion, incest, etc., nor do they need explicit commands to take care of the environment, the poor, etc. The creation ethic that is inferred from the text carries as much authority as a direct command carries; and hence, whether there are further prooftexts, which would merely exist as examples of applying such an inferred principle, is not relevant to whether one is capable of condemning what is contrary, or practicing what is supportive of, the inferred creation ethic the text communicates through those means.
So I don't need a prooftext against contraception. I don't need a prooftext against homosexuality. I don't need a prooftext to argue that we need to be concerned for the poor and the environment. If I have one, great. If not, so what?
One also can't slither out of the text and its applications as easily once this is understood. One can make some argument that she's doing a good by dating an unbeliever, and not technically disobeying the command to not marry one; but such a practice is of the sphere of disavowing one's allegiance to the Lord, it is a disobedience of the inference that such partnerships and all that surrounds such partnerships is evil. The text becomes something that is merely promoting a principle to be inferred and applied in every which way that it can (as long as it is understood within the context of the whole counsel of God).
The most important thing I would say, and I will end with this, is that seeking the inference and all of its applications is an act of love toward God and others. If my wife told me she wanted to bake a cake and asked me to go to the store to get her ingredients, I would infer that she meant all of the ingredients and buy all of them accordingly. I would not merely go and buy two ingredients and say that I've done good enough. "Good enough" is the law of obligation that we don't really want to fulfill. It's doing what I really don't want to do. It evidences no love for my wife and only concern for what I want to do. In contrast, seeking the best and to do above and beyond what is explicit is the law of love. It looks for good rather than looking to avoid it. It seeks to do all that is pleasing to God rather than get away with what is considered "good enough." This is why the excuse that the people practicing anomia "lawlessness" (understand lawlessness in terms of the above, not in terms of what is explicitly disobeyed) in Matthew 7 give to Christ (i,e., that they were in ministry and doing some good things for Christ) doesn't fly. It is not their willingness to fulfill obligations that damned them, but their lack of a loving relationship with God that made them unwilling to seek His favor as their Lord in all things. It is the attitude that gives a little in order to steal a lot. They wanted to be their own lords and be saved in the end too. Such cannot be, as a truly loving relationship with God through the Lordship of Christ is the only path to life. And that is why one can only be a Christian by seeking the applications of the inference.