I assume you are referring to the OP. (And that is great, because the thread has gotten far afield of the original question.)
As to reasons proposed for HOW young earth creationism has become an obstacle to the Great Commission, here are some of the most cited reasons:
1) The Apostle Paul said that believers should focus on the Gospel of the Cross of Jesus Christ "and if I preach any other gospel, let me be accursed." Are creationism ministries a needless distraction?
2) Young earth creationism and the "creation science" it has spawned have tended to associate Christianity (in the minds of the general public) with science-illiteracy and ridiculous folly, such as Ken Ham's Creation Museum.
3) YEC websites are known for dishonest quote-mining, misuse of science terminology, and misleading and erroneous use of both the scientific and Biblical evidence. (As a result, "Lying for Jesus" has almost 300,000 hits on Google.)
4) YEC leaders and their followers have become infamous for strawman arguments--which even non-believers cite as violations of "Thou shalt not bear false witness."
5) We know that the earth is billions of years old and that God used evolutionary processes to diversify and adapt life on earth because God filled his creation with enormous quantities of evidence which tells of that history. YEC believe that God's Bible is a reliable source of answers about history but that God's Creation is not. Neither the Bible nor Science supports that claim.
6) Young earth creationism has tended to present a false dichotomy: "To be a true Christian you must choose between the Bible and Evolution." There are other false dichotomies often presented but that is probably the most common one.
Many are concerned that young people are forced out of the church by a fork in the road which they should never face. If people consider the Gospel to be associated with pseudo-science, they will decide, "I can't ignore common sense and the weight of the evidence. If I have to reject scientific facts to accept the Gospel, I can't live in that kind of illogical state. So if accepting the Bible includes accepting young earth creationism, I guess I must reject the Bible."
There are others but these are probably the most common reasons.
Thanks for reminding us of the thread's purpose!