Yes. There are side effects such as Myocarditis, but these are also the issues that someone with covid would have, except far, far worse. If you suffer Myocarditis from the shot, then you were very probably going to experience significant cardiac issues from a full blown covid infection.
On the one hand, it stopped a huge viral outbreak on the original variant. We already know (and there is no point in dismissing) that long Covid is a problem. These numbers would have been far higher if the virus was allowed to freely circulate with no mitigation. We would face significant population health, social and financial issues now and the numbers would totally overwhelm the HSE (who can't cope with the current workload right now).
On the other hand, there is an health impact from cancelled OP visits, cancelled screening, and social impacts from school closures.
The latter however, we know how to tackle, even if the resources may be lacking The former....its scary to see how little is still know about Long Covid and some of these peoples lives are ruined. Crank the numbers up and it becomes terrifying. These people can't work, and are a burden on the healthcare system.
On balance then, the right decision was made, especially early on when we knew nothing about the short, medium and long term impacts of covid.
Yes. There are numerous studies on this, both at a population effect level, and at a basic level in measuring droplet counts expelled using a mask and without.