It is true that Christians are told to rebuke evil and to have nothing to do with the fruits of darkness (Ephesians 5:11). But the problem is that when people start using argument based on guilt by association, it is really going to create a lot of major problems. Remember that pagans also have invented non-religious stuff we use today like the Gregorian calendar (invented by Pope Gregory XIII), the Pythagorean theorem and the Hippocratic oath to name a few. To dismiss something all because of its source is to commit the genetic fallacy theory. The same goes for guilt by association which might be safe to say both arguments are often inseparable.
To say that something is wrong because pagans do it does not truly measure towards the Word of God as a standard. When it is said learn not the ways of the heathen, it does not mean that you do not drink milk because heathens do it, you do not wear eyeglasses because Pope Francis wears glasses, you do not eat German franks because Benedict XVI loves to eat them. Instead, it is not to learn the ways of the heathen where you learn their ways that goes against God. Sometimes, some things merely coincide while others happen to be a conspiracy. Certain signs and symbols may or may not mean the same for certain people like how a thunderbolt may represent Zeus for pagan Greeks but it may also mean danger high voltage for electrical companies. A fish logo may mean a worshiper of Dagon but it may also mean the fisherman's club.
Some Christian apologists today spend too much time researching on conspiracy theories than going with scholarly methods. While I do agree there are conspiracy theorists who are truly born again Christian, they have a strong love for unbelievers and they want to see them saved but they tend to have a wrong approach in preaching the Gospel. Some Christian conspiracy theorists do have the desire to win Roman Catholics to Christ but their methods tend to only make the people they desire to win to Christ too angry to listen to them. While the message of salvation should not be softened up but if Christians should offend unbelievers, it has to be offending them with biblical truth and not with the approach of being as cheesy and offensive as possible. It can be seen that this method of being as cheesy and offensive as possible tends to throw in a horrible generalization towards people. It is just like assuming all Roman Catholics and Muslims are criminals in the fallacy of division instead of taking on the general truth they are people who are victimized by false teaching.
Getting out of the conspiracy theorist approach in favor of a scholarly approach is not easy. What is really needed is in witnessing to unbelievers, one should invest in a scholarly approach like studying more on church history and exegetical study of the Bible. The whole battle to save the souls of men is not too much on what the atrocities of the Vatican and the Illuminati. Instead, it is all about preaching to lost people the good news. I remembered the time I was told that I was too fixated with the lies of Satan rather than the grace of God to defeat the lies of Satan. While one needs to know the lies of Satan but the other part must focus on the grace of God. Using a stronger knowledge in Scriptures makes one more able to witness than having known a lot of curious events. It is really time to focus more on focusing on false doctrine and how to correct them with Scriptures taken int context as the best way to witness to the lost.