Ethics are a very personal thing....
I have a personal hate on for the 30-30, always have.... Don't like lever guns much either... Let's call it a biproduct of spending too much time in my younger days dogging deer out to old timers with 30-30 levers and witnessing way too many wounded deer, which I was then left to track and finish off..... When I first joined here, I went off the rails on a big rant about how I didn't think the 30-30 was an "ethical" choice based on the fact that we have so many "better" cartridges available for use now and the 30-30 only became popular because the rifles were cheap and ammo was everywhere..... Quite frankly, I made myself look like a complete tool ranting on about how crappy the 30-30 was.....
Fast forward 5 years and not much has changed (except for the fact that I try not to look like a complete tool most days)... I still don't like the 30-30, even though I reload now and could get one up to respectable velocity.... I still don't like lever guns much based on those experiences in my past and I don't ever see that changing.....
What has changed, mostly due to interactions with good members here, is that I can acknowledge that a 30-30 is perfectly capable of taking a deer cleanly and ethically if used within it's limits and with proper shot placement and it is some people's choice.... I have come to the personal realization that it is not up to me to define what is ethical or not ethical for anyone but myself.... I do have lines in the sand like most.... Taking low percentage shots being one... Perhaps if those old timers had taken the time to place their shots properly and not fire off 3-4 shots in the direction of a deer presenting a Texas heart shot I would feel differently on 30-30... To me, there is no argument that can be made that taking a low percentage shot is ethical....
So, with the 38-55 being legal for deer, I would turn your question back to you.... Do you feel the 38-55 is sufficient?, Are you confident that it will kill with a well placed shot knowing your own shooting skill? Are you willing to hunt within it's limits?..... If your answer to all 3 is yes, then I say fill your boots.....