This debate is getting good! It's time for me to get serious! (or at least as serious as I can at 12:11AM!)
Your argument is that even though Shinichi and Ran share the same morals, their interests differ too greatly for them to be together happily. I think otherwise. Morals dictate what you believe in, and essentially how you'll live your life. If they share the same morals, they share the same wavelength, and are more likely to understand each other in times of crisis. (when these crisis' don't happen to involve the complexity of teenage emotions- nobody understands those.)
As far as backgrounds go, I don't think how you're raised has that much effect on your love life. I'm raised in a strict household that requires the best academic standards and participation in academic events, and I could fall in love with someone who grew up in a casual family that puts emphasis on sports. I'm not saying it wouldn't affect the relationship at all, but backgrounds don't really have as much as an effect as morals do.
And interests... Yes, that deciding factor. *sigh* Let me put it this way. Shinichi and Ran wouldn't be best friends (for like what, 10+ years?) if they didn't have some common interests, whether they've been revealed or not. I'm just pointing that out. One interest I know they share for sure is an interest in each other- and that alone counts for a ton. To be that interested in another person means you listen to them, you know and want to learn things about them, and etc. etc. Asking questions about each other's interests and learning about the other person and becoming interested in their life makes up for all those lost interests.
As for 'truly loving' something as you define it... For one, centering your life around a person and always putting them first is a very unhealthy lifestyle as it makes you unstable and ruins the rest of your life as well. And secondly, truly loving someone doesn't mean you're not allowed to pursue your passions and put them second for a little bit as well. Shinichi puts his cases above the importance of a date. I'd put my math and science competitions above a date too, and I wouldn't be dating a guy who didn't understand they are important to me, The fact that he tries to resist shows he cares, the fact that Ran tells him to go shows she cares as well. If you don't call it 'love', then let's at least call it 'mutual attraction.'
Chasing after Vodka and 'abandoning' Ran isn't as big a deal as everyone makes it sound! It's a case of 'curiosity killed the cat.' Shinichi is a detective. When he sees weird things, (especially if these weird things are suspicious) his natural instinct is to go investigate. If Vodka was just trying to find a friend that got seriously lost on the way back from the bathroom and Shinichi helped him, we wouldn't say he 'abandoned' Ran, would we? The thing that leads people into that way of thinking is the consequence of his actions, being shrunk into itsy bitsty Conan. Just imagine he made a mistake. Does it look so bad then? And if it does, are you trying to say you're not allowed to leave the side of a person you love because you want to check something out? What if you were at a museum and you wanted to see two different exhibits, and didn't want to see the other? Is it a betrayal of love if you don't go with each other for ten minutes? The final result just makes Shinichi a lot worse than he seems, okay?
The part about marriage just made me crack up... Shinichi would investigate what he wants and still be able to spend time with Ran. No couples are together even close to 24/7 simply because of the hindrance of jobs and personal affairs. You're allowed to have a life outside of marriage. And Shinichi does not just go randomly around Tokyo looking for crimes to solve (crimes find him. ) so it wouldn't be like he'd never have spare time. If he ended up working for the police, he'd work police hours, if he was going to open his own agency, he'd work Mouri's hours. (with less beer, cigarettes, and Yoko.)
That's my side to this. :3 Now I'd better get some sleep before I'm just a walking zombie tomorrow. See ya!