Question: I've seen biblical proof-texts used to support both right and wrong doctrines. How should I respond to the person who argues that, "You can just prove anything...so why bother?"
Answer: Proof-texting is problematic for the very reason shown in your question. People use out-of-context biblical citations to support out-of-whack doctrines. So, in a way, your disagreeing friend is right. People will use their pet proof-texts to support one side of an argument while their opponents will use their pet proof-texts to support the opposite side...so it all sounds like a waste of time, doesn't it? Truth be told, that is a waste of time. Fortunately, there is a way to cite Bible verses that is not a waste of time—and that's good news. Because using biblical citations is still an important tool to use when discussing God's word, and we should not stop using citations just because some people use them wrongly.
I have found that people in general do not realize just how context-sensitive our language really is. We can't even define a word without understanding its context in a sentence. That is why dictionaries have multiple definitions of the same word; they have to cover every context, and the words in the Bible are no different just because they are in the Bible; they also take their meaning from the context. There is a cute saying about proof-texting that goes, "A text without a context is a pretext for a proof-text." And that describes the problem exactly.
A cardinal rule of Bible interpretation is to always consider context. How specifically? First, we need to find the context within the sentence. Next, we need to find the next greater context—like a paragraph or the complete thought of that portion of Scripture. Then we go back even further considering the entire book, the section of the Bible, the author, and the audience. No Scripture is free from the bounds of its targeted culture, nor of the time of its writing, nor of the idiomatic constraints of the original language, nor of its order in the progressiveness of revelation. Only after we consider this full range of contexts, can we understand our Scripture passage, and only then are citations meaningful.
Furthermore, Scripture should be studied as it was written: In order, one line after another. That's how God served it up, and that's how we should eat it. Don't get me wrong, topical study does have its place, but it should never replace the process of verse-by-verse exegesis. That method of study helps keep the context straight, and it also helps prevent those leaps into aberrant doctrine.
Additionally, an earnest bible student should consider the arguments of those who hold opposing views. We should pretend to be them for a moment and study the topic from their point of view (as much as possible—and having weeded-out the ridiculous claims). If we pursue an earnest study from an opponent's perspective, then we will be in a better position to evaluate their proof-texts. We will either be "converted" to their position, or else better understand why we do not subscribe to it.
Yes, this is a lot of work, but I would hope that a true believer would consider this time well spent. Although time-consuming, the result of such study is that when you deign to cite a passage, you will have earned it. You will not have picked it up from somebody else's list of verses, a gospel tract, or a web site. The citation will be between you and the Holy Spirit. This is the type of study the apostle Paul spoke about in 2 Timothy.
“Do your best to present yourself to God as one approved, a worker who has no need to be ashamed, rightly handling the word of truth.” (2 Timothy 2:15, ESV).
Even in Paul's day there were plenty of people wrongly handling the word of truth. The New Testament is replete with warnings against false teachers in its letters, and I'm sure that these teachers-of-error were proof-texting from their favorite ancient documents.
Prayerful study is the way through, but prayerful study is a process and not a result. We will likely change our minds on many issues as we mature in Christ and as we become more familiar with his word, and along that gradient we may assign proof-texts weakly or wrongly. The trick is not to use proof-texts. Instead cite Scripture that is the result of careful and contextual study. In so doing you would not be relying on an isolated text to make a point, but rather you'd be using that text to point back to a fully contextual truth. Legitimate scriptural citation and proof-texting may look alike on the page, but the proof-texting purports to make the point, while the legitimate citation announces that Scripture has made the point—and here's where you can check it out for yourself.
So, how would I respond to someone who doesn't wish to engage in a discussion about scripture because he sees proof-texting as problematic enough to stop the whole show? I'd respond by affirming that the discussion of God's word and the furtherance of God's truth is worth any amount of trouble. We must, however, understand the limits of proof-texting. It is context-sensitive whereas truth is not. Truth is truth—and in God's economy truth is what gives everything else context. Therefore, citations that reflect God's truth are legitimate and the rest are not, and we must not abandon our search for the truth just because some neglect due diligence. That would be a win for Satan.
“Jesus said to him, “I am the way, and the truth, and the life. No one comes to the Father except through me.”
(John 14:6, ESV).
Frankly, I'd rather be dead-wrong about some doctrine than insult God by abandoning his word on the grounds that a scholastic methodology seems like a waste of time. We will never "get" everything that God put in his word, but that should never stop us from trying. Nor should it stop us from taking a strong stand even though we may later be proven wrong. Remember, great and godly men stand on opposing sides of many biblical issues, and we'll likely have to wait until heaven for the final say. While we remain on earth, however, the Christian life is more about the process than the product. Keep praying and studying—and be brave! Do not be afraid to take some scholastic risks.