I think the answer depends on how a person defines chastity - and whether the person holds importance to being chaste until marriage.
I am not passing judgment - or suggesting that anyone take this view...I'm just sharing a different angle...
In my home we teach chastity and definine it as reserving a sexual relationship (a physical, emotional and spiritual thing) for marriage. Orgasm is a part of - and the climax of - the sexual relationship.
We do affirm the joy (physical, aka orgasm) and benefits (spiritual, spousal relationship-wise and procreational) of a sexual relationship, but that all are to go together.
...so masturbation is a form of seeking a part of the sexual relationship (orgasm) outside of the sexual relationship.
Thanks for listening (if you did

)