I don't quite understand what you're trying to say. It seems to me you're trying to portray religion as some kind of a supreme law to which all men are somehow bound. As if religion is something that binds us together and if that thing is gone then all chaos ensues. For me, that's not how it goes.
Let's break it down real quick:
Rape would be good because instinct tells us that we are sexual beings.
No, because there is something called law that prevents people from doing whatever they want. However, law =/= religion the last time I checked. And yes, instincts tell us that we are sexual beings, but rapes will, unfortunately, happen regardless of the existence of religion. Some people are born sick in their minds or become so through various circumstances and going up to them and saying "Jesus wouldn't want you to rape this woman" isn't going to prevent anything.
Let's define laws: Crash walks down the street and stabs a homeless guy. Good, bad, or neither? Atheists will say it is "bad" but Crash can always argue that it isn't bad to him.
The key word here is "laws". Again, you mixed up laws with religion
So sure, you can stab a homeless guy, but the police won't ask you "Sir, are you aware that you did a bad thing because God said it was?" Nope, they will arrest you and you will be tried and punished for your crime. Religion won't play any part in that. And sure, if you're thinking that religion can help you with your moral standing, I agree that it can. But it's not like people would go out and stab each other in the streets if there were no more religions in the world.
If you don’t believe in a god, what stops you from committing crimes?
Laws, your upbringing (how your parents raised you), etc.
If you're atheist, isn't that just like being religious? You can't prove God doesn't exist...?
Hm, but who can prove that God(s) exist? I'm not aware of anyone who has died, went to Heaven for example, met with Jesus and God, then came back to Earth and said "yo it's all real, they all exist"
It's all what's in your head and what you choose to believe, which is totally fine for me. But this can be a question to an endless debate, where religious people and atheists will cancel each other out.
I want to get married in a church or buried in a churchyard - so how can I do that if I'm not religious?
If you don’t have to follow any religious rules, don’t you have an easy life?
Well there are various loopholes when it comes to that. For example, I know that in Serbia you can get married in a church as long as you are baptized and as long as you "declare" yourself as an Orthodox Christian. So if I'm with a girl who's religious and we want to get married in a church, I'll just declare that I'm Christian as well (even though I'm not practicing any religion) and that's that. As for being buried in a church yard, I hardly think it's possible unless you are a priest or something... But I get your point.
All in all, what I'm saying is that people are free to believe in what they want, but believing or not believing in something
doesn't make them impervious to laws. That is why we have them, because they don't care which religion you're part of as long as you act like a good citizen and a contributing member of your society.
