I have no problem with people who deny the Oral Law, whether they are Karaites, Samaritans or Gentiles. But I don't like it when people deny it and then want to quote it partially. If soemeone denies the Talmud, he must be honest and use his own sources only.
I don't agree with all the teachings of the Talmud but it is related to Tanach. I also use Talmud (even Zohar) for research purposes (eg. the topic of tithing). Christians don't agree with all writings of historians Flavius Josephus but we use the statements of Josephus extensively in our circles. Why do we need to use our own sources only? For research purposes we can use anything. Christians apologists use Talmud (even Koran) to justify that Adam, Eve, Abraham, Moses, David and Jesus were indeed historical figures. It depends on the context and the subject of the discussion. Even Tovia Singer in his lecture about the oral law tries to use the Christian New Testament to prove the existence of oral law (audio 11:40). Muslims, Christians and Jews when argue with each other quote "favorable" verses even from their opponents' scriptures. I have heard Chaim quoting the saying of Jesus in John 4:22 (Salvation comes from Jews). For research purposes we can use any material.
Yes, it's correct to use a material you don't believe in as a religious book, only for historical research. I also use even the Quran to get an idea of the Arab life-style of the time, because all books have at least some historical hints. But using the religious parts of the Talmud about what is a sin without believing it is a Divine Law, is senseless. You cannot choose to agree with one part and reject the other. If you do so, it shows you don't recognise any spiritual authority in it, and there is no point in using its authority to back your own views.
For example, I hold that gambling is a serious and dangerous vice which destroyspeoles and societies. The Quran backs my views and claims to be inspired by G-d. But I would be an hypocrite if I quoted those verses to back my view, because I am not a Muslim and so I don't believe the Quran is prophesy. I can only read it to learn about the History of Arabs.