On the first, we can and do work together. The problem is that the issues that separated us way back have not been addressed (or can't be addressed), and that we no longer speak the same theological language our forefathers did. Hence we have threads like these, where everyone chases each other round and round and never really gets down to the basic assumptions that cause us problems.
On the second point, you are right. Cicero said that no society has ever rescued itself from decline after the decline started. Things are only going to get worse, and the best we can hope is to preserve some part of the culture for the next generation.
Each individual has their own unique truths of faith. That's because these truths are learned and we all receive it differently, no matter how consistently taught. Therefore, we all have our own perception of the Lord. To argue it is meaningless.
It's funny, as a Swedenborgian we believe in the Trinity of Person in Jesus Christ but we reject Sola fide. Here on FR, I tend to agree with Catholics more than not on the important stuff - how we live our lives according to our faiths. Meanwhile, a good number of protestants who seem more concerned what a person thinks than any charity in their hearts.
In Matthew:
22:36 "Teacher, which is the great commandment in the law?"
22:37 Jesus said to him, "'You shall love the Lord your God with all your heart, with all your soul, and with all your mind.'
22:38 This is the first and great commandment.
22:39 And the second is like it: 'You shall love your neighbor as yourself.'
22:40 On these two commandments hang all the Law and the Prophets."
If we all kept this in mind as Christians, we could do a lot to move forward. Swedenborg writes that loving your neighbor does NOT include attacking their beliefs.