" but I don't agree that altering the welder that I own should be a federal crime"

Altering plenty of things is a federal crime.

You can't file the serial number off a gun, for example.

As a more apropos example, you can't make a sawed off shotgun. it is a federal crime to possess them, and this includes making them, without paying some tax and registering for a permit.

If you want a less violent example, most medical devices can't be modified, etc.

"We're changing the very definition of property here to support some company's price discrimination scheme."

No, we really aren't. While completely controlling everything you can do with every physical device you own is a great theory, it's definitely not reality, nor has it been, for many many years. It's definitely not "the very definition of property".

In fact, historically property law was worse. If you physically mutilated or damaged some things you owned (religious, etc), you could often get stoned/killed.

"The grand purpose, though, is upholding the notion that when I own a thing that means I am free to do I want with it."

You are working off the premise that this changes the state of the that. It does not. That is because this notion has never been upheld, and i can point to tons of examples of physical property you can own but are not free to do what you want with.

Your examples of changing weapons to be untraceable or more lethal are not apropos because these are violations of legal restrictions passed by congress into law.

You can not saw off a shotgun not because Browning doesn't want you to saw it off, but because sawed off shotguns are not legal.

What the DMCA does is take a manufacturer's prerogative and elevate it to the status of federal crime as soon as the manufacturer decides to create a "digital rights management" scheme to enforce that prerogative.

"Your examples of changing weapons to be untraceable or more lethal are not apropos because these are violations of legal restrictions passed by congress into law. "

So is the DMCA?

I'm not understanding what distinction you are making. They became federal crimes identically.

"You can not saw off a shotgun not because Browning doesn't want you to saw it off, but because sawed off shotguns are not legal."

I'm not sure how this is relevant, particularly? What relevance does who wants you to not touch your property matter to your notion you should free to do with your property what you want.

"What the DMCA does is take a manufacturer's prerogative and elevate it to the status of federal crime as soon as the manufacturer decides to create a "digital rights management" scheme to enforce that prerogative. " I'm quite aware of what the DMCA says (and in fact, have been directly involved in pushing back on large numbers of crappy DMCA requests).

I'm trying to understand why you think this is special somehow, compared to all the other things that folks have made it illegal to do with your property, which span the gamut from government saying you can't do this directly, to government saying you can't do what this other guy says you can't do, to etc.

The DMCA's anti-circumvention language constitutes a delegation of congressional power to private manufacturers, who can create schemes at will to criminalize uses of their products which they consider to be harmful to their business.

"The DMCA's anti-circumvention language constitutes a delegation of congressional power to private manufacturers, who can create schemes at will to criminalize uses of their products which they consider to be harmful to their business. " ?????

No it literally does not. You make it sound like they choose what is circumvention and not, and they don't. Congress did. You are really stretching here to try to differentiate it. You'd be much better off saying "it's not different, but it still sucks", because right now, your argument strongly stretches credulity IMHO.