I think Twitter is so unique and so large that there is room for people on all sides of the fence. I do not consider people who promote their listings as spamming, because I only see their posts if I follow them to begin with. It's my choice to see their tweets or not. Personally I like seeing listings from other artists, as I like to see the work that's out there. My husband is on the other side of the fence. He uses Twitter to connect with people he knows already, and to follow news and sports feeds. He would be much more likely to be annoyed by links to store items.
I personally don't see Etsy listings being banned from Twitter, they would have just as much reason to ban any of the other self-promoting segments on the service. I would never tell someone else that they should not promote their listings through Twitter either. The fact is that Twitter will bring more views into your shop. Yes, I agree that we all should use common sense about how we tweet our items. Generally, there should be some general dialogues going on, aside from self promotion. And generally, it's a turn off to see a long queue of listings in a row. But it's a learning curve, and people will do what works best for them, and we're all free to develop and implement our personal philosophical guidelines of who we follow and why.
I value my network, especially the handmade artisan core of my network. Don't be afraid to show off your work, because if you don't someone else will. I don't mind!