My fear has never been rebasing itself, but that I make some kind of mistake with a random change conflict and don't notice it because it's not tested for directly. But I'm also not sure if that's categorically a git fear. (Edit: related to this, I think this sort of minor "itchy worry" is grounded in how sometimes conceptually simple diffs look messy during conflict resolution.)

If all I'm doing with git rebase is reorganising my commits, and I have to deal with conflicts, after I'm done, I always git diff my pre-rebase head with post rebase head commit hash. I can quickly see I've messed something up if the diff isn't empty. For more complex tasks it's best to leave the rearranging until last, but where not possible, the diff is still pretty useful to double check my work.