From concerns regarding their safety (see the quality control issues with Chinese vaccines), to nefarious government intervention (such as unethical medical trials) to concerns about espionage and data collection ( see the CIA and their vaccines as cover for spying in Pakistan and Afghanistan).
To say "there is no reason to ever question or be against vaccines" shows a disturbing ignorance and naivety on how the world works
Would you prefer "There is no reason to question vaccines produced to FDA quality guidelines based on established and well-accepted efficacy, completed within an ethical and rigorous set of clinical trials"? Because I'm pretty sure that's what people generally mean when saying "there is no reason to ever question or be against vaccines" even if they don't state that explicitly.
Those things mentioned, to the extent they exist, are tiny nits on the enormous benefit. They are always discussed in isolation complete with heart-rending horror stories of suffering and no countervailing presentation of massive benefit of vaccines. It's a common tactic of subversion - essentially "how to lie with facts".