After nearly 2,000 years of trying, traditionalists still haven't persuaded even a bare majority of the world’s population that Jesus is the only way to God, let alone that God himself said so, as claimed by some). Even in the United States, one of the world’s most religious nations, only a fraction of the population is persuaded by that claim: A 2005 survey of 1,005 Americans, conducted by Newsweek and BeliefNet, indicated that 79% believed that a good person of a different faith could attain salvation.
Think about that two-millennia track record; contrast it with, say, the track record of fluoridated water supplies. In the 1950s, as fluoridation was just starting to catch on, some branded it a dangerous plot to subvert traditional values and beliefs (much as was said in certain precincts about early Christianity). In a matter of just a few decades, however, more fluoridation studies were done, and more evidence was accumulated. It took not even a half-century to persuade Americans that, on balance, fluoridation is a reasonably good bet. Today, according to the Wikipedia article on fluoridation (which has been the subject of an editing battle between pro and con points of view), "66% of United States residents on public water supplies have fluoridated water” and “In 1998, 70% of people polled believed community water should be fluoridated, with 18% disagreeing and the rest undecided.”
My point isn't that fluoridated water is or is not a good thing. It's that the dispute got resolved comparatively quickly, because most people were willing to take a sober look at the evidence, to face the facts, and to move on.
So now let’s look again at the claim that Jesus is the only way to God, and the ancillary claim that God himself said so. If either claim were true — and especially if both were true — it seems likely that a loving God would have made sure we knew about it. In particular, you'd think God would have arranged for the supporting evidence to prove at least as persuasive to the world's people, over the course of 2,000 years, as the evidence in support of fluoridated water has proved in less than 50 years. That doesn't seem to have happened; yet some traditionalists keep stubbornly insisting that their claim, despite its overwhelming rejection, is a necessary part of all right belief.