There are ideas about doing that with some gel type substance to capture junk. Unfortunately, a large metal object doesn't work as the collisions may occur at relative speeds of hundreds or thousands of km/hr. At that speed you mostly just smash things into pieces and send the careering all over. Unfortunately that hurts more than helps.

Also, that mass would be huge and cost a ton to put into orbit.

I have worked in space debris tracking before. I'm not forgetting anything. Low LEO clears in a relatively short period of time, it is not at serious risk. High LEO...I mentioned? You seem to be freaked out that I didn't mention a specific term that's become overly common amongst those who don't understand the environment.

The most serious risks to High LEO are what I mentioned: ASATs and breakups of non-operating satellites. If those continue to happen unabated for some time then we can start to worry about Kessler Syndrome. Too many people watched Gravity and took it as a real risk.

Maybe? Some older intact satellites may be of some value with more reliable in orbit servicing. Outside of those though, not so much. There's little infrastructure to recycle parts, and the cost of doing so would greatly exceed launch costs.

The short and medium term path needs to be developing infrastructure to keep orbit cleaner (deorbiting and refueling old sats).

It remains a resolvable problem. There are only a handful of orbits where it's a longterm issue. At low LEO orbits are cleared as drag pulls debris in for reentry and MEO/GSO orbits are pretty big and remain mostly uncrowded. High LEO and GEO is the real issue, particularly GEO. If parties with launch capacity now were mildly responsible that's not a huge issue. The key is moving satellites before they break up and not testing ASATs.

That's pretty doable if certain countries could not be totally irresponsible.