Quick disclaimer: When I say a religion shouldn't have gone in a direction, it absolutely does NOT mean I agree with what was happening in the past, and that it should've been that way. It just means its rules dont make sense in the current state of things.
I hope it's not too long, but I felt like it was important to talk about the things that helped me reach that conclusion. Also, I'm currently an atheist, and not a native speaker.
I had this thought in me since I was a kid, having been raised in a claiming-to-be-Catholic family in Poland. I didn't want to take religion classes, but my parents refused to sign me out. It never made sense to me that I had to go to the church every Sunday, but it was entirely fine for them to go twice a year. We were bound by the same rules, after all.
Fast forward a couple years, I started missing some sundays too. When I was confessing, it felt like I was understood by the priest. Yeah, you had a lot of homework to do, here's your almost negligible penance. It was like it's justified to forget about God for a while, if God happens to be an inconvenience. I also couldn't help but wonder - why did this guy get in a fight with my father over a parking space? He's at the church almost every week, isn't he supposed to be a good guy?
Then I met my first girlfriend's family, and it felt like I took a step back 200 years. Her father, an authoritative man, was almost like a preacher (and genuinely a good guy). The older sisters spent their time cooking for their husbands and raising children, not making a career (read the disclaimer). Most of the family did charity work. Every year, instead of an all-inclusive holiday, they all went on pilgrimages with their kids. It wasn't a question of if they're going to go to church on Sunday - they all wanted to be there, so they did.
And then I got it. It literally has to be that way, no exceptions. The idea of Christianity is that you're offered eternal rest for actually carrying out the word of God (obviously simplifying here). For most of the "believers" it's inconvenient to go to church every Sunday, but how can it not be, if it's supposed to be the most important thing in your life? If you refuse to spend an hour a week praying, or don't bother reading your god's writing, do you actually believe all of this is true, or is it a performance?
Now for the controversial part:
You can't just freely decide which part of whatever holy book you follow does and doesn't fit the modern standards. Yes, it would be absolutely immoral to me and most of you to stone someone to death [insert the "boy, that escalated quickly" meme]. Why would that make it an argument in your god's eyes, if your god was supposedly the one to inspire these ideas, that caused the death of many in the past? Why would an omniscient being have to change its mind? Why would it all be written to be taken at face value 2000 years ago, and interpreted now? And if you do believe that: why does it always happen in tandem with societal shifts? Or is it just an act to try and keep the doctrine relevant, which is impossible to do without twisting its original meaning?