> Slavery was also considered above-board at one point, so...
It was also perfectly constitutional[0], hence the need for that 13th amendment. And that civil war thing. As it turns out, the constitution kind of sucks[0], it has a lot of problems with it. Fewer than it did in the past, but we aren't quite at the end of history just yet.
You're going to need a better complaint than 'it's unconstitutional', as this is pretty verifiably constitutional. The people who have been empowered[1] by the founding fathers to determine what is, and what is not constitutional have determined that this is constitutional. It's not a matter of opinion at this point.
> carrying private service X is required for you to exist in the united states.
And that's nothing new. Government can compel all sorts of things from you. Showing up to contribute your labour to a jury duty. Involuntary servitude in the military. Taxing the land you live on. Following emergency orders. Not heading a communist political movement. Every society - even this society - provides you with privileges, and requires obligations from you.
This obligation has been ruled to be well within the legal framework of this society, and if you think it should be outside that legal framework, you should look into passing a constitutional amendment on the subject.
Or, you could believe that this obligation is a constitutional, but bad idea, and have the legislature repeal it. Either way, it's currently constitutional. [0]
[0] You're confusing 'constitutional' with 'just'. They are not the same thing.
[1] Actually, SCOTUS' powers in this sphere are what's unconstitutional[2], but we all close our eyes, and collectively pretend that they are.
[2] You're not going to find anything in either the constitution, or passed legislature granting SCOTUS the incredibly broad powers it currently enjoys. These powers were invented out of thin air, and are backed by neither fiat, nor democratic will. All that the constitution says on the subject is 'We should, like, probably have courts. That should do stuff, maybe.'