What many people miss when they advocate for boosters is that antibody count is not the full story. When it comes to protection against severe disease, cell-mediated immunity is key and doesn't go away.
Here's the most relevant science I've found about the effectiveness of the booster.
https://www.nejm.org/doi/full/10.1056/NEJMoa2115926
If you look at the results table, the booster does benefit everyone. I can't argue with that. However, the absolute counts shown in that table paint a more nuanced picture.
While the 60+ crowd gets significant benefits from being boosted, making it a no-brainer for them, the under 60 crowd has less benefit. The under 60 crowd is already relatively safe from severe disease and death with the original vaccine dose.
Being healthy and under 60, I need to weigh these mild benefits with the cons: 1) normalizing mandated boosters as an ongoing way of life and 2) extending the pandemic by using up booster doses instead of sending them to undervaccinated countries (the ones where new variants are popping up).
Instead of getting in the habit of being boosted with the same vaccine every 3-6 months for mild benefit, I think it makes much more sense to take a holistic view that helps us end this pandemic.
[Edited for clarity]