The logical implications of age of accountability view:
1) not just one exception to the rule all have sinned (like Rome with Mary) but now millions even possibly billions of exceptions to that throughout history based on those who were born and didn't make it to that age
2) not just a few mortal sins as to walk away from salvation but now all sins are mortal sins when one comes of age
3) for those many who never make it to that age and never sin in that view, then Christ never died for their sins since they don't have sins needed dying for, hence Christ didn't die for all but just those of age.
4) two ways to be saved, by grace through faith for those of age and by being below such age
Doctrine matters. A wrong view on one issue like this touches on other biblical themes.
Here we stand.