It is well known that the vaccine reduces fhe spread of the virus.
Yes, if everybody has the vaccine it is much more likely that the spread of the virus will be prevented/lessened.
But its not the main aim of the vaccine.
1.
Prevent death - it does this for the vast majority of people
2.
Prevent serious illness - most people who have two doses are protected from this. Their natural immune system is usually enough anyway, even without a vaccine, so two doses on top is more than enough. However, it does wane so having boosters first and foremost for people in certain age ranges and then vulnerable groups is crucial, absolutely.
3.
Prevent infection - the vaccines help with this, absolutely, but it is not the actual goal of them first and foremost. The most effective prevention to infection is either a) avoiding social contact - i.e. not realistic, or b) having got COVID already and having natural immunity. The vaccines on top then add another layer of protection. Now the more people who get vaccinated then yes, the more that helps with dropping infection rates right down.
The argument for boosters is a sound one. But rather than talk about how everybody needs a booster, let's focus on getting the people who really do need one done first, ey?
I've had COVID, I've had both jabs. I feel lucky I'd had one jab when I had COVID. I was still ill, and still aren't fully right, but I'd had one jab. The second jab set me back massively when I had it, but that probably was because I'd had COVID in between the doses. It wasn't nice though and as a fit 26-year-old I will admit even I have a bit of trepidation about going to get a booster given how crap I felt for weeks after the second jab. I'll do it if I have to, though I don't feel any particular rush to.