Andrew So I wonder what makes them reject the view expressed by mainstream medicine and psychology.
Truly there is not "mainstream" medicine talking about It. There are some articles, but mainly related to male masturbation, there are not medical evidences about any benefits of female masturbation.
Relief sexual tension, strength vaginal area, sleep well... are not benefits, since they are small, exist other ways to achieve those, or are unnecessary in most of girls.
Sexology is the "science" that touches more the topic, and obviously it has an important basis bias.
Andrew but none of them apply here...
No, certainly there is better motivation an reasons.
I share most of thinking of my uncle, but I think that exist another reason, it reinforces the path of behavior, setting and accomplishing the prohibition, it is obvious that all bad behaviors of a sexual nature move away from us.
I am not saying that this is nothing set in stone, and there are girls like @Sin or @Kaja who have another philosophy ans it's perfect for me, I do not say my morality is better, but I do not want their life for myself.