We know quite a bit about their short term safety. It's impossible to know for sure if there is any long term side effect. But that is probably a risk we have to take to get past the immediate threat of covid-19.
Do you have an actual source for that? People keep repeating it over and over but I've seen no evidence that COVID-19 carries particularly high risk compared to other infectious diseases.
IMO the risks of an rushed new vaccine are much higher
If this is indeed the point of contention - balancing the risk of adverse outcomes from a rushed vaccine vs those from a virus, I think it's inaccurate to say that the risks from this virus, understood generally across the population, are "very high". The likelihood of contracting it is of course very high, but the risk of adverse effects are only high for a relatively small stratum of the population.
It makes sense to reserve "very high" for pathogens like HIV or Ebola, not SARS-CoV-2. For a very large majority of the population, SARS-CoV-2 has approximately equal risk to the four seasonally circulating coronaviruses, so even a small risk from an overlooked data point might be significant.
We need to reach herd immunity one way or another, so I'm not sure the discussion of individual risk is the right one. With no data being available for patients to examine ourselves, it's hard to even know how to make these decisions.
The fatality rate of COVID-19 and the rate of serious complications is high enough that it easily dwarfs the chance of any potential rare side effects of the vaccines.