If marriage is "just a bit of paper" and "it's no big deal" and "it doesn't change how he feels" then what's the problem doing something so inconsequential that would make your partner happy? This is the argument that blows that shit right of the the water.
Like, it bugs my DH that I screwed the lids back on the tetra pack when recycling as it's inconvenient when he's squashing it into the bin. to me, it's "just a bit of paper" and it's "not a big deal", right? But I'm happy to leave the lids off if it makes his life slightly easier.
So the argument that marriage is nothing is false. It isn't nothing and he damn well knows that.
What he's actually saying is that he's fine with the inequality in his favour in your relationship as it stands.
That he's fine with you having less protections and access to joint assets than he does in the event you split.
That he's fine with you having less chance to build up your social contributions, your career and your pension.
He's fine with living his life every day making yours minutely inconvenient because, ultimately, he's benefiting.
So, what you do is work out what you need to earn equally. You'll need to go full time of course, and childcare duties and responsibilities will be strictly 50/50 As will every other single house and family expense and things like appointments and parent teacher meetings. Housework will also be strictly 50/50. Your future financial security is as important to you as his is to him. You can no longer afford to be a stay at home mother if unmarried.
I was very lucky when TTC that my GP directed me to MN and this board. I wasn't married, and DH wasn't bothered, so right through pregnancy and the baby years, even now I work full time. Now, I'm lucky, I got a good man who always pulled his weight with the baby and the house and was generous with the finances and continued to do so but I saw on here how quickly that can change in the most unlikely candidates. I'll never be at the mercy of any man financially - ever.
He's shown you who he is. Time to show him who you are.