It is rare these days, at least in my experience, to meet a non-Catholic Christian who believes that doctrinal differences actually make a hill-of-beans worth of difference in whether a person ultimately makes it to Heaven. Rather, in modern American evangelicalism, the message pretty much seems to be: “We’ve gotten beyond all of those petty doctrinal disputes. If you want to make it to Heaven, all you need to do is just love Jesus.” At the same time, though, the various Protestant denominations, with all of their various doctrinal peculiarities, continue to persist: Baptists (“Baptism is just a symbol but it must be by immersion!”), Lutherans (“Infant baptism by sprinkling is just fine!”), Anglicans/Episcopalians (“Elizabeth II is the human head of our church!”), Methodists (“Yay, Arminianism!”), Presbyterians (“Yay, Calvinism!”), “non-denominationals” (“We’re just Christians!”), house churches (“Acts 2 says the early church met in homes so that’s what we do, too!”), etc. This state of affairs begs the question: if it’s all about “just loving Jesus,” why don’t all of these groups (who agree at least on that point) get together as one big “church”?
This is when things get complicated for a Protestant: how do you justify being divided from other self-identifying Christians (by not worshipping together, by supporting different (and often competing) mission work, etc.) and at the same time assert that the things that separate you don’t really matter to the one thing that is the entire point of the Christian faith–making it to Heaven? One possible answer to this is to appeal to the mere fact that the divisions have existed for some time and, simply because of that, somehow have become natural in this “fallen world” of ours. In other words, you can appeal to tradition. But that in and of itself is a problem for Protestants who claim to reject Catholicism–because a standard criticism Protestants have of Catholicism is that Catholicism relies too heavily on “tradition.”
Another thing you could do is take a “different strokes for different folks” position in which each of the various Protestant denominations corresponds to a particular personality type. Thus, for example, you could maintain that Presbyterian churches are for the more cerebral, while the Assemblies of God are for the more emotional. The problem with this approach, though, is that there’s no indication Jesus intended for there to be different types of “churches” for different types of people. St. Peter and St. Paul obviously had very different personalities. But they were members of one Church.
All of this points to a really big problem for modern American evangelicalism that (at least to my knowledge) it has yet to really grapple with: the fact that, while it more and more downplays the importance of doctrine in the pursuit of a “just-love-Jesus” sloganism, the Catholic Church continues to insist that doctrine isn’t just the subject of a somewhat diverting parlor game but actually matters, both to how we live life here and now and to our eternal destinies. This puts the individual, just-love-Jesus-type evangelical in a “Pascal’s wager” type of position with respect to Catholicism. Is he willing to take the chance that he is putting his soul in danger by deliberately holding on to the doctrinal peculiarities of a given Protestant belief structure that is contrary to Catholic teaching, when he himself doesn’t believe that, by adopting a Catholic belief structure and becoming Catholic, he would be doing anything that would put his chance of making it to Heaven in danger? In that situation, isn’t it almost just common sense to submit to the claims of the Church? What, other than inertia (or maybe the fear of discomfort) could hold the “just-love-Jesus” evangelical back from the Church? I, at least, can’t think of any reasonable basis for holding out in that circumstance–again, assuming the evangelical we’re talking about here believes that Catholics can make it to Heaven (just like “born-again” evangelicals can), a possibility that almost all modern-day evangelicals would admit.
As someone who, up until last year, was a fairly typical modern-day American evangelical who had gotten used to the muddle of the “I’m OK, you’re OK” approach to all intra-Christian doctrinal disputes, I fully sympathize with any readers out there who are put off by the starkness of the Catholic Church’s claims. It is startling to be told that the Catholic Church, in all seriousness, continues to assert: (1) that She is the Church Christ Himself established, in time and in visible form, when Christ walked on our Earth; and (2) that to refuse entry into Her, when one knows She was “founded as necessary by God through Christ,” is to put one’s immortal soul in jeopardy. I fully get how disconcerting that is. But how could it possibly be worth it to take the chance that you’re wrong–and the Church is right?
 I recognize I’m painting with a fairly broad brush here, as there certainly are Protestants who continue to believe that doctrinal differences matter in some way. In this regard, I have heard stories of Protestants driving half-way across the country to tell friends considering conversion to Catholicism that, if they take such a step, they’re on their way to Hell. Such Protestants, however, seem to be very much outnumbered these days, at least in the United States, by those Protestants who do not contend that the various doctrinal issues that divide Protestants from one another (or all Protestants from the Catholic faith) actually matter.
 Please recognize that I’m not saying that, if one is not formally a Catholic, one is necessarily headed to Hell. That is not Catholic teaching. I discussed this issue, and what the Catechism has to say about it, here. Also, if you’re interested in this subject, you must listen to Deacon Sabatino Carnazzo’s lectures on the Church’s teaching that “outside the Church there is no salvation,” available here.
 “Pascal’s wager” is a classic apologetic argument in favor of belief in the existence of God: it’s better (and more reasonable) to believe in God and a system of eternal rewards and punishments than not to because the gain in so believing is infinite while the gain in not so believing is virtually nil. For more on Pascal’s wager, see here.