To my mind, the "give her my brand" bit is not beyond the normal range of traditional chauvinist rock-n-roll metaphors--it's not worse than, say, "Tire tracks all across your back, I can see you've had your fun," not to mention any song that mentions "using my gun" where an actual firearm is not meant. And the jumping-on-top-of-her stuff is just playing out the seduction-object-as-wild-horse metaphor. For me, the one really skeevy moment is the way McGuinn says ". . . a fahhn lady."
The problem is that the metaphor bleeds over into the thing it's a metaphor for (ha ha). Songs about screwin' where they mention guns, the gun doesn't become part of the sex act. It's one or the other, either the song is explicitly about coitus and how much the singer likes it, or it's about *wink wink*shooting a gun*wink wink* because implicitly saying "I'm going to fire my gun, because I obviously bring a gun to all my love making sessions so wear glasses and some ear-protection" is creepy. But you can't have a universe where this guy is chasing a horse, and then say "She'll be like a wife" because that implies that in this universe, there are horses and there are women. And women become wives. But this guy doesn't want a woman, he wants a horse, but he's going to treat that horse like a person.
That is the product of a sick sick mind, and I would say that Roger McGuinn needs counseling, but he wrote the dang thing with a psychiatrist, so I think this might actually be a legal matter. Bunch of horse loving perverts.