It's neither speculating nor catastrophising. The risks are real and documented. A confused child cannot give informed consent in this situation:
"The primary risks of pubertal suppression in gender dysphoric youth treated with GnRH agonists include adverse effects on bone mineralization, compromised fertility, and unknown effects on brain development."
"GnRHa therapy prevents maturation of primary oocytes and spermatogonia and may preclude gamete maturation, and currently there are no proven methods to preserve fertility in early pubertal transgender adolescents."
"The primary risks of pubertal suppression in gender dysphoric youth treated with GnRH agonists include adverse effects on bone mineralization, compromised fertility, and unknown effects on brain development."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5290172
"GnRHa therapy prevents maturation of primary oocytes and spermatogonia and may preclude gamete maturation, and currently there are no proven methods to preserve fertility in early pubertal transgender adolescents."
https://pubmed.ncbi.nlm.nih.gov/31319416/