Taking your points 1-by-1:
> So you want them decrease their risk from 0.2% to 0.1%
The linked study said those that had gotten a booster had 10% of the risk of those that didn't, so using your first number it would be like 0.2% to 0.02%.
> Expires in a few months
It's unknown how long the booster would last, or if after the booster the recommendation would be to move to something annual like flu shots.
> They've already had a history of reacting to (further shots always worse)
The person I responded to didn't say what their reaction was, or if it was time limited. Also, "further shots always worse" is demonstrably false, I know a couple people who had bad (yet, again very short term) side effects with the second dose and barely anything for the booster.
> No one takes liability for
The US government specifically runs a National Vaccine Injury Compensation Program, https://www.hrsa.gov/vaccine-compensation/index.html
> Relatively has higher risk of side effects among their profile
The person I responded to didn't mention this
> Unknown long term risk
Vs. the now well-known long-term risks of contracting Covid, which given its prevalence seems highly likely that your long term choices are (a) never leave your house, (b) reduce likelihood and severity of infection with a vaccine, or (c) get Covid.