You got me on that one, except that public masturbation is indecency, which takes away a parent's ability to use public facilities with any expectation of comfort. There is really no substantial societal difference between public masturbation and fondling of other people without their consent. I believe what is being legislated with those particular rules is the affront to others with socially unwelcome behavior. This law is also particularly used and enforced where no general expectation of such behavior exists. For example, a public nudity statute would be unenforceable in a strip bar, as a general expectation of such behavior exists there, so it is unlikely that a person's sensibilities will be affronted. This doesn't exist for example, at McDonalds. There is a reasonable expectation that a visit to McDonald's will not result in the viewing of public fisting of a walrus. That's reasonable. If you had a sign in front of a business that said "Come in and witness the public fisting of a walrus" then such behavior would not run afoul of most statutes other than the animal cruelty. (Animal cruelty laws ARE inherently altruistic). So actually maybe you don't have me there. Most public decency laws actually are a reflection of expectation and are similar in wording to assault laws (not battery). Remember that assault is unwelcome speech or behavior which is delivered in a beligerent or impertinent manner, and is generally intended to hurt, cause discomfort, or offend another person. It is intended to cause HARM. Notice the similarities with decency law?
I find it highly offensive and hurtful when the government teaches my child that homsexuality is equal to heterosexuality. Honestly, I would rather run into a flasher than two men making out on the street. When everyone starts defining everything for themselves, when there is no community standard allowed, then one person's indecency is another person's right to free expression. At some point you've just got to allow the community to define what is decent for themselves. Unless a town has a population of 1, these things affect everyone.