The current "conversation view" is misnomer. There really is nothing like that. Again, just think of Gmail and how it's handled there. This is how it would look like, e.g. you actually see your own response, too. Currently this is impossible because Thunderbird does not actually know what messages belong together. It just applies some ugly hacks to even find the ingoing emails. It's a trainwreck, but I believe it will get better and we will finally have some decent mail software out there.