Why do my comments keep getting sent to trash?

SP does sometimes have small hiccups so maybe that is the reason. The OP also has the ability to send comments to trash as well as the admin who has the power to delete comments/posts.
OP’s can moderate/edit comments as they see fit. Sometimes threads go off topic or a controversial topic is raised in which case removal is easier than the potential outcome.

I did read both your replies and am sure that your approach regarding your parents outlook on mental illness is starting to prove successful based on your mums change of position.

Ideally everyone would base there opinions on fact as the current evidence demonstrates. I know my position is always fluid, anyone has the ability to change my position as long as they supply the relevant evidence. But part of what makes us individual is that we all think differently and maybe this is a good thing, it does often challenge us.