Apparently Kant opposed masturbation as immoral: "That such an unnatural use (and so misuse) of one’s sexual attributes is a violation of one’s duty to himself and is certainly in the highest degree opposed to morality strikes everyone upon his thinking of it."
Another example of opposition: Alabama restricts the sale of sex toys. Not the use of them, mind you. Just the sale for profit.
Why do I consider this issue? I'm considering the issue of self-morality, e.g. what obligations does a person have to himself and what is the source of these obligations. E.g. suicide, body modification, and masturbation are three examples that come to mind. Many moral philosophers define "morality" in contrast to self-interest, meaning that moral issues are primarily if not entirely about the relations between an agent (self) and other agents (or the rest of the world, as the case may be--if one wants to include for consideration acts on inanimate objects).
Now suicide often has repercussions for others, e.g. survivors. Hence it is definitely a moral issue in the above (other agent) sense. Body modification may be considered a moral issue if some argue--rightly or not--that its public display is persuasive (e.g. for young people to emulate). But private masturbation? Here it seems that there are few arguments against it. Perhaps one might argue against the sale of tools for such purposes, as in Alabama (e.g. children might see these tools in stores). But Kant argues that masturbation is immoral in and of itself (in terms of some duty towards self and species I guess).
My main point in noting this issue: While many moral philosophers considered "morality" to be a relational issue (e.g. how our acts affect others), Kant is willing to define "morality" in such a way that private acts that affect nobody else are also wrong. Not unlike the biblical tenet of Matthew5:27-28: that one can commit adultery through thoughts, not just deeds. Hence a morality of thoughts, not just actions.
What do I think? I'm not sure. Just examining one of the edges or extremes of moral issues. More later.