Sects was probably a bad term to use - some people only use it with a negative (Christian) implication, whereas sects are quite accepted as a reality in many other religions; but I am using it in its neutral, technical sense - a subdivision. To my understanding, Sandemanism was a sect, but no less true or valid than most of the others.
I've certainly observed Christians around the world clearly behaving as though they are on the same page, and I can say the same for Muslims and a great many other faiths. The mental state you describe as 'saved' (oddly enough) is again something which they all seem to achieve - even the ones that many would consider to be 'invalid' expressions of their more obviously central faiths.
By 'true', I assume you mean core/near-core or embracing a critical mass of traditional ideas, whether or not the Bible is considered the actual or the inspired word of God? Perhaps it's easier to work the other way round - can you describe where the line comes between true and 'other', or what Must be involved in order to be considered True?
I'd also love to get closer to articulating what 'almost identically' looks and feels like and whether it is genuinely different to the mental state/attitude of mind that devout people of all faiths experience. Curiously, 'born-agains' appear to achieve an enhanced version of the 'saved' state, as far as I can tell. Care to have another go? I'll try to help, but I need a few more clues!
Interesting isn't it. As an industry, religion has many products, some of obvious virtue, some dubious. I think it can get a bit patchy at sect level however. Anyway, the impact of the good stuff is such that rather large numbers of non-believers do good stuff routinely because it happens to be the proper thing to do - and not because they expect to get rewarded for it after death. There was an age when it was very hard not to be a churchgoer in England, because there's be stigma - your sin could be responsible for the lack of rain. The converting priests were very skilled at using public opinion against recalcitrants. In England today, I suspect far more charity money comes from non-believers, tho I haven't done the research. It would be interesting if the same pattern were seen elsewhere.
Most share a common delusion that the Bible is divinely inspired, when archaeology and textual analysis have proven otherwise. Most also share gender bias, persecution of differing religious traditions, and opposing scientific progress.
On the other hand, many Christian sects have helped lift millions of people out of poverty through charity work. Also, Christian based counseling services have helped individuals through all kinds of personal difficulties. And, many Christians have used their personal wealth to start hospitals, schools, shelters, and other institutions that have strengthened society's safety net.
Suffice to say the religion has been a force for both good and evil, at various times in history.
True Christians don't have "sects". We all believe the same way that I know of. Something happens to us when we are "saved". Suddenly, were all on the same page. It is hard to explain but most true Christians believe almost identically the same way.
PS. Does the Bible advise on how to achieve the 'saved' state, apart from the implication of the 'filled with the Holy Spirit' moment?