With respect to climbing mixed & ice routes within an alpine setting on public property; are there ethics addressing protection like hammering pins?

Is it acceptable to lead a mixed/ice route placing pins as necessary?

Assume that for the sake of this post, there are no land management concerns either prohibiting or regulating climbing protection.

What is good style for a lead?

Definitely acceptable. In alpine and ice, pins are always acceptable. Nature of the beast, don't fall, and don't die, do what is necessary.

Just got my pins back out today!

Mark, IMHO, there is so much freeze-thaw in areas that form water ice, that pins are hardly an "ethical" issue in this form of climbing. Rock climbing is a totally different world. In Vail, whole blocks fall off routinely on mixed routes (see Secret Sickle). Alexander's Chimney, RMNP, is a good example of where you take anything on a mixed route. If you're referring to your photo/my comment at Lincoln on the left variation to Scottish gully (since you posted a photo about my comment), I didn't pound pins; however, with the ice as it appeared to form, I thought that an average idgit, like me, in certain conditions, might find rock gear hard to trust, ice screws impossible to trust, and pins the only sane options for pro. You are climbing on a 2nd pitch there. The best thing for a climber is to be able to come back another day to climb. Funny, turns out we did another pitch that day, I did this little pillar up and left. No pins. Couldn't find a good anchor to be below. My partner popped his tools, and I wound up with contused legs as I got dragged down into my anchor and basically did a flip. Peace.

Leo, yea thanks for looking into this. My pic & your comment just happened to be coincidence only.

John & I happened upon that section by getting out of the bowling alley to that right set of bolts, we looked to the left sidewall and said, it looks like it could go; and we found, the climb was good. We saw another tube to the right that was even harder, but don't think we could have gotten it on our first day out.

We then had a conversation when we got done: Man, a couple of pins to lead a rock pitch sure would be nice to have. We were actually looking at another different problem up there when we thought about using pins (an overhanging dihedral). But then we talked about having everyone up there seeing me bang the rock without understanding that nuts, cams, & tri-cams just weren't going to work. Is it cool or not to bang away? I guess in this venue, pins are acceptable.

When I don't have pins on the lead rack, one of my favorite pieces is the hammered in nut. Just watch your load direction.

There is only 1 rule to remember..
there are no rules..

Hell yeah pins are acceptable. I climbed a route in Canada once and the pillar was too chewed up to get a screw. I wasn't going to climb it without pro, so a pin it was. Whatever it takes to save your ass.