Actually it depends on what you think is "meaningful". It could be having children, but it also could be discovering a new vaccine, helping other people, or just living a happy life without annoying anyone.
In any case, even if one thinks so, I find it quite rude to say that having a kid is the most meaningful thing you can achieve to someone that may not have children ...
Bitter defined as 'a sense of unjust treatment', is absolutely correct, but 'angry, hurt, or resentful'... nah, none of that.
In fact, quite the opposite, I'm extremely happy about my decision to not have children.
I'm just not a fan of people who think that it is the most meaningful thing I (or anyone else) could ever do.