Thicker bear line that WON’T hurt trees?

I'd advise just helping the weight along on the way up and supporting it on the way down. That will be easier on the tree than just going with a thicker line. Use your hand when in reach and a stick or trekking pole when above your reach. It is the sawing action that is the problem and that can be pretty much eliminated if you keep the weight off of the line while pulling it up or lowering it down.

That is assuming you are pulling the weight up by dragging the line over a branch. If pulling the weight with the line passing through a pulley, ring, or carabiner it is a non issue.

If you are already doing that I really don't think the damage to the tree is significant enough to worry about if there is any at all.

I have been helping the weight within my reach, but I had not thought to use a pole from there. That is good advice, thanks!

I use bear cables when available, but that has not been often.

You mention the line passing through caribeaner instead of over the tree limb. Is there a way to rig that so you can put it up and take it down for a limb that is 20 ft in the air?

Like stated above:

Toss one rope over the branch with a carabiner knotted in the middle of the line, with your second "hauling" line threaded through that biner. Once the two ends of the primary rope are secured to two different trees (using cut tubular webbing around the rope touching the bark), you now can easily raise and lower your gear, without creating any friction on the tree.

Of course the likely fact that you are hauling up a small amount of weight up reduces the impact on the tree as well.