Sola scriptura leads to pluralism.
Sola scriptura (literally, Scripture alone) was a rallying cry of the Protestant Reformation: Scripture (the Bible) is the highest authority on all matters of theology. More specifically, sola scriptura means that the Church, which was believed to have had the authority to interpret Scripture (and Tradition) definitively, did not actually have this authority. This means that the Reformers did not believe that there existed an authoritative interpretative body to interpret Scriptures for us. But this is no problem, they said, for Scripture itself is the authority.
But there is a problem: Scripture is a text. All texts require interpretation. It is not possible to just read a text or get at it's plain meaning. Different individuals will have different perspectives, different levels of acquaintance with Scripture, and different backgrounds when excountering Scripture.
Even during the Reformation, different Reformers interpreted the Bible differently. Luther didn't fully agree with Calvin who didn't fully agree with Zwingli.
Someone must be some sort of interpretative authority or no one could ever believe anything the Bible says. When there is no authoritative interpretive body (such as the Church), the individual is left as the final interpreter of Scripture.
It might be easy to see how this leads to Pluralism.
Because different people interpret Scripture differently, with no authoritative body to which to make an appeal, Protestants have split over and over and over. Some put the current count of denominations in the world at 30,000. But of course this is merely division, not necessarily pluralism.
Christians who grow up in such an environment realize that this is a problem for them. What does the Bible say? How can I have any chance of interpreting it correctly when there are so many people who are smarter than me who have studied more than I'll ever be able to study who disagree on basic matters of theology? What does a person need to believe to be a Christian?
Christians also realize that such a large amount of disunity isn't good either. Christians should be united, right?
Protestants have two options: fundamentalism or pluralism. Either you think that your particular permutation of theology must the right one for no other reason than it's what you have gotten out of Scripture, or you concede that the points where there exist disagreement don't matter. Since fewer people today are willing to believe that their particular non-denominational church that was founded 2 years ago is the one true church, people often opt for the second option.
And so, too often today these problems are solved by conceding as unclear and therefore as unimportant any theological question that seems to have disagreement among people who call themselves Christian.
Few people, especially those of my own generation, have strong theological convictions beyond that we need to follow the Bible and we need to follow Jesus, (and even that is sometimes questioned). Beyond that, they don't know. More than that, they'll probably think that you're an arrogant bigot for thinking too definitively that anything is true Christian teaching. It's okay if you have your opinion, but that's all that it is: your opinion. Don't try impose your opinions of what Scripture says on me. I don't think Scripture says that. And since we are both supposedly basing our beliefs on Scripture, we should be content to disagree and accept our different beliefs as different ways of seeing Christianity. Thus, it doesn't matter if you're Baptist, Lutheran, Anglican, Methodist, Presbyterian, or attend a non-denominational church. Hence, pluralism. (Just don't be Catholic, because that particular permutation is for some reason absolutely horrible...)
To be clear, I do not believe that the problem rests with Scripture. It is a result of sin that Scripture has become unclear for us. I also do not believe that no one is able to get anything out of Scripture. Many times, most of us agree on what Scripture is basically trying to say. But what do we do when we do disagree which, from experience, happens all the time? The Protestant answer has been to either split and/or say that that point of theology is no longer important.
Or did God have a better plan? If God was going to give humanity his final and complete revelation in Jesus Christ, would he not also have provided some means of safeguarding it?