There are benefits for the state being involved. But the right to marriage isn’t something given in the constitution of many, or any governments. The right to form a contract between two people are.
I rather not, because you are giving the state the power to regulate and redefine it.
But since it is, I understand the benefits of it like stability to faintly units and incentivized having children which is pretty important. Also seems a bit discriminatory towards none married people.
Mosaic law? I believe people should be able to put whatever the hell they want in their mosaic!
To address a few specific points…
There is. 
Now ask yourself, is Turkey a Muslim country? Is Indonesia a Muslim country? Was Egypt a Muslim country from 1923 (or whatever year it was) to 1980?
Then there’s the strange case of Lebanon…
While we’re at it, is Thailand a Buddhist country? (Answer: technically, no. Also technically, it’s a democracy. 
)
I repeat: yes, religion matters; no, it’s not sufficient to explain the state of the world.
No, it’s not the same with every other country. (I assume you mean every Muslim country.)
Countries have this habit of pulling strings in other countries. Muslim countries do it too, absolutely. Is there a religious angle when they do it? Yes, of course. Is that sufficient to explain the situation? No. You need to understand geopolitics. If religion (or a specific religion) were sufficient to explain it, the meddling that all countries of any stature do would be proportional to how religious they are, or in your paradigm how Muslim they are. Where’s the evidence for that? (Not anecdotal evidence, because that just gets countered with more anecdotal evidence.)
I really think you don’t understand humanity as well as you think you do.
Try this. You have two children. Due to a crisis, at least one of them is going to die. If you don’t choose which one, they will both die. They are both very similar in age, health, etc. A few days ago, you discovered evidence that (1) one child may be wavering in his/her faith, and (2) you may not be the other child’s father. Which one do you save?
You don’t need to tell me your answer, of course. Maybe it’s one, maybe the other. The point is not about you personally; it’s about humans in general.
As for national identity in the Middle East, Africa and Asia, it’s a complex topic. To some extent, national identity overlaps with ethnic identity. To some extent, ethnic identity overlaps with religious identity. To some extent, religious identity overlaps with national identity. It’s complicated.
For example, remember that (alleged) genocide in Myanmar? Muslims are not the only ones who have faced extermination there in the current decade. There’s also an obscure ethnoreligious group (the name escapes me) who are basically indistinguishable from the Rohingya, except that they happen to be Buddhists. Why do you suppose the exterminators lump them in with their Muslim cousins?
You make it sound like the Troubles are ancient history, more ancient than your terribly important Xth sack of Rome. I know some of us are older than you, but not that much older.
Of course, religion alone is not sufficient to explain NI either. If it were, any place with a similar mix of Protestants and Catholics would have similar “troubles” of its own, and NI would still be a war zone today.
You know what’s boring about this discussion?
(1) It’s like arguing with a missionary. Or like arguing with that American who wrote an anti-China book about 15 years ago, with the message that China is has a feasible plan to take over the world, they’re the biggest threat ever, they will never accept capitalism because they’re the most hard-core Marxists ever, bla bla bla. (Yes, I said about 15 years ago.) And I get it. I read the news. I know what goes on in China, as much as the next alien. And I don’t care. By which I mean I care, but not in a way that’s going to stop me from having Chinese friends, enjoying certain aspects of Chinese culture, and even visiting China from time to time, without fear of being murdered or Communized or fed dog meat. I’m just not as easily frightened as some people, whether the subject is China or Islam.
(2) Unless I’m forgetting something, you haven’t told me anything I hadn’t already heard, apart from
If it’s just going to be more “what about IS?” type posts, I’m not interested. Not because I think those things don’t matter, but because I have other ways of gathering that kind of information and analysis, without quite as much nonsense mixed in.
I hope some of the things I’ve said have been interesting to you. If not, it’s hard to see how continuing the discussion would benefit you.
Do you like game theory? Maybe you’d find that more interesting than my deconstruction posts.
I’d like to leave you with two film recommendations. They’re both about that strange case in the Middle East, Lebanon, and they’re both relevant to the stuff we’ve been talking about, though not in terms of “whose religion is the best/worst”.
(Don’t read the articles btw. Spoilers matter.)
Hope you enjoy them! 
What if it’s anti-cow hate speech? 
It is no longer a democracy. It’s a military dictatorship with a psychotic king.
Believe me, I’m already inured to it. They keep calling what comes out of my udder a symbol of “white supremacy.”
Technically = de jure. They got a new constitution last year! 
I think that based on this thread, the answer is no.
The constitution was suspended by the military junta and that new one you refer to legitimizes all the actions of that junta and is backed by the psycho-king. Democracy seems to be on the wane throughout S. E. Asia.
To be fair, it never had a very deep hold there to begin with.
Marcos famously once said that maybe, just maybe, democracy is not the form of government best suited for S. E. Asia.
Are you trying to say unicorns aren’t real? 
Well, if the junta says they’re real then they’re real.
In related news the junta is forming it’s own political party to run in the upcoming elections. The party will be endorsed by psycho-king. But voters can make their own minds up…