It's a word with implicit implication. Careless people are thoughtless. Selfish people are thoughtless. People who don't give a damn about other people are thoughtless. Praise is never intended when calling someone thoughtless. It doesn't seem like there's ever any good in being thoughtless. It's bad without exception.
I can think of an exception.
The literal meaning of thoughtless is: without thought. Having no thought for others is certainly bad. Being thoughtless about certain other things isn't so bad.
You might be thoughtless about getting praise You might be thoughtless about getting credit for what you do. You might be thoughtless about a lot of things that are usually called virtuous.
There's nothing thoughtless about that kind of thoughtless. Virtue almost demands being thoughtless of self.
There is another kind of thoughtless I'm guilty of, though I don't feel guilty about it. I don't care what people think; by that I mean, I don't have any personal stake in the argument, belief, or certainty, of anyone. They think what they think. I think what I think.
I don't think that's a problem.
In fact, I think that sort of thoughtless mitigates problems. I listen better without an axe to grind. I'm more interested in understanding than competing. Interlocutors needn't reach agreement to make discussion worthwhile.
My thoughtless indifference to different points-of-view doesn't mean I'm thoughtless about whether the points-of-view are good or true, and it doesn't mean I'm indifferent to what's important to someone else. It doesn't mean I'm not listening.
I listen, without emotional engagement.
Some find that annoying. I'm sorry.
I probably couldn't change even if I wanted to; neither am I trying to change anyone else. I've no interest in that. I do enjoy sorting through ideas.
Whether an idea is true or false, enlightening or disappointing, isn't as important to me as truly understanding what's being contended. Combat with a straw-man is pointless.
Understanding an argument is more useful than winning an argument.
People think what they think. I think what I think.
I don't intend to irritate anyone with my thoughtless emotional indifference to their point-of-view.
At least I listen.
That's not thoughtless.