I am aware of the context of the "Syllabus of Errors". Then Pius IX should have been careful to put it in context. Instead, it was interpreted by the world at the time (and still) as a condemnation of democracy and freedom of religion. Frankly, I think scholars will overwhelmingly agree that Catholicism's endorsement of religious freedom is a modern phenomenon. It had little alternative in this democratic era.
Some years ago I was in Spain, when Franco was dictator. Franco, Mussolini and Hitler, by the way, all were baptized Catholic - which doesn't mean that much, because there have been bad leaders among Protestants, too. Anyway, while there I did a little study of religious conditions (something I continue to go when I visit places). Protestantism was not permitted freedom of religion, except in a couple places like Madrid where nations like England and Sweden had their embassies and an Anglican and Lutheran church were tied to those embassies. Elsewhere, Protestants had to worship furtively. In visiting a pastor I found in Barcelona, he told me how he could not have any sort of outside sign to identify his church. He ran a small seminary - four students - and these were studying secretly and he brought me to their hidden classroom. Now, of course, Spain is wildly secular - even permitting same-sex marriage. In fact I rather think that Catholics may be, on the whole, more liberal than Protestants. One recent US poll showed that all three US Protestant demographics opposed same-sex marriage: mainline Protestant by a couple % points, evangelical and Black Protestants by wide margins. Catholic Americans, however, endorsed same-sex marriage, though also by a close margin. Suggests the lack of influence of the hierarchy these days among Catholics.
I am a senior citizen, vitally interested in religion, hopeful that it can be a bridge instead of a barrier. There are bigots among Protestants, especially fundamentalist Protestants, who regard Catholicism as a pagan cult. But most Protestants I know are ready to respect Catholicism as a different expression of the same Christian faith. The major problem is that traditional Catholicism doesn't see Protestantism that way. The hierarchy preaches that that church alone is the one true church and thereby promotes prejudice against Protestantism. Sad.
The one true church rests in our hearts and souls. I know you don't believe this but I find that most Catholics, certainly those I know, reject the bigotry and exclusivism of the past. We have so many intermarriages and such these days (as in my family) that our churches can no longer rally us against one another. I am alarmed that there is so much resentment - plus misinformation - evident here on CAF. I feel like starting a new forum, a new blog, or whatever, inviting people of goodwill, regardless of their faith, to discuss ways and means of leaving behind bitterness and prejudice from the past. As I have said, my heritage is in 'both camps' - Protestant and Catholic. One key figure on my family tree was Archbishop of Canada 200 years ago.
But some people apparently seem to need self-esteem, so they believe they are part of the one true church or the one true political faction or the best of all nations in the world. Well, I tend to believe the latter, too, though I'm sure that God doesn't have any preference when it comes to the diverse peoples of the world.
God bless you and everybody out there.
You see, we believe that the Church speaks for God, and we believe that whatever God says THROUGH THE CHURCH is the last word. 
