A. These are the most researched vaccines ever.
B. The pseudo argument that you don't know the long term effects, while theoretically true, doesn't take into account that basically everything has long term effects, that they may be negative, positive, mixed or neutral, and that they vary from person to person. Some people thrive under vegan diets and some quickly become malnourished. Same for the extreme opposite: a protein based diet. Some people tolerate sun well and even require it for vitamin D, and some get sunburn and cancer.
C. The newer variants are all of more contagious, more severe and more likely to both infect and be dangerous for young people. Again, selection pressures make this to be the likely trend onwards.
D. Don't take shelter under statistics. As said countless times here, by far the greatest life danger for minors in the USA and other developed countries are drowning and car accidents. Yet we are not forcing parents to avoid pools and bodies of water or to avoid having their children ride in their cars.
E. Don't take shelter under statistics. A lessened probability, which again, is increasing through viral mutations, isn't zero probability. The same way some people who are 100 years old have recovered. And the same way young people have recovered from infection but retained long term negative effects.
F. Again it isn't zero probability. My cousin, who was in his thirties, was never a smoker or a diabetic or obese, and worked a physically demanding job so de facto exercised basically everyday, died with relative ease. Take the risk if you will, but don't say it isn't a risk. And unlike stuff like smoking or drinking the risk isn't exclusively yours. Of course even those may harm others through passive smoke or through drunk interactions but you can minimize those easily.
G. The pseudo argument that it is gene therapy is simply unscientific. Something between 7.5% and 20% of our genome are already viral genes. You may more than double that with prokaryotic genes and those coming from other eukaryotic species. Unprotected sex gives you a tiny amount of your partner's cells and thus genes. To argue about the vaccine being gene therapy is simply ignorance of basic genetics. Not that genetics is very popular now in the SJW era, certainly.