"You will then have the freedom to do whatever you want each and every single day, and won't have to spend all that time and energy constantly convincing someone of things that are often for their own good."
I wish!
Constantly convincing someone of things that are often for their own good is basically the definition of what you do when working for yourself, or should I say when your working for you clients/trying to acquire new clients.
Imagine building a business that passively generates half of your yearly spending. Now you just need to generate the other 50% of your yearly spending from "active" projects like jobs and medium-sized clients. It's not full independence, but I'll take it over being completely beholden to someone else.
It's not childish to take responsibility for your life, to carve your own path and gain greater degrees of autonomy. In fact, it's what fully developed adult human beings do.
When I talk about being self-employed I like to say that I traded having a single "boss" for multiple "bosses"-- one or more from each Customer. One thing that I've really enjoyed, to that end, is being able to cut my losses with a given Customer if the situation becomes untenable. That option wasn't so easy when I was an employee. An employer, in most of the US at least, has the freedom to be fickle at any time for arbitrary reasons. Being self-employed, to my mind, helps to level that playing field.
Being an employee amounts to running a business with a single Customer. If that Customer leaves you've suddenly got a business with no Customers. New Customer acquisition costs are very high (especially in the employer-provided health insurance world of US employment) and Customer loyalty can be very low. It's a precarious situation to me, not one I'd ever want to be in again, and not one I'd counsel someone to put themselves into.
As long as you work under someone else's supervision, you will never have the freedom to do whatever you want, like for example give a conference talk or a million other things.
I'm sure it's not only the conference talk, right? There are other things. Instead of investing so much time trying to navigate the relation with your manager and always ending up in situations like this, I suggest trying to use that same energy and effort and dedicate to try and find a way to become your own boss.
You will then have the freedom to do whatever you want each and every single day, and won't have to spend all that time and energy constantly convincing someone of things that are often for their own good.