> You think we are physically unable to build an asteroid defense?

Mate the dino-nuking asteroid that hit Earth was 10km in diameter. Even if we launched every nuke we had at such an object, it wouldn't do much to deter such an object. And that's assuming it's moving at a low enough fraction of c that we could actually detect such an object in time to mobilize all said nukes.

So, no, I don't think we would be able to defend ourselves today (nor by 2100, let's say) against such an adversary. Same deal with any species that is sophisticated enough to do interstellar travel. For them it's even easier, they can just pick up a few rocks from Kuiper belt, stick some mass drivers on them and it's bye-bye Earth within a few weeks/months.

> (and we are doing a lot)

The point is we're not. We haven't even reached peak fossil fuel yet. Even if we stopped everything tomorrow, things would still keep getting worse for at least another few decades. But as it is we're reading today about how bad we made things for ourselves in the 80s. Since then our consumption has only continued to accelerate, which can only mean things will be even worse tomorrow.

> but if the counter to everything is: not enough, doomed anyway

No. That's not what I or anyone else in this thread has been saying.

It's like this. We are on the Titanic. Some very clever people have charted our course and done ocean sonographs and determined there's a big-ass iceberg ahead. Many folks like you are insisting either a) there's no iceberg or b) icebergs are good for ship hulls or c) we'll out-technology the iceberg somehow and thus we don't need to worry about the iceberg. So right now all we've done is ACCELERATE towards the iceberg. If there was sensible suggestions like "let's alter our course slightly" I wouldn't be saying "well that still puts us on course for the iceberg so there's no point". I would be saying "great! that's a start!".

Well, I can see how you don't see that we are doing a lot. Thankfully that is not distracting people from doing.