But if you never use that address again how is that useful information? 

If you're talking about ordering something to be delivered to you you have to give up your physical address no matter how you paid for it. 

My point is how does bitcoin compromise your identity?

I mean figuring out who you actually are.  Amazon is a bad example because you have to give up your identity anyway.  I am saying how can you find out who somebody is if you never use the same address twice?

ok lets say the government have cloned the data on a drugs website. they see that  an anonymous seller that has not listed his home location address but has withdrawn funds to address 1XTr45ecr3tAddr355BlahBlahBlah

the government can simply google search:
1XTr45ecr3tAddr355BlahBlahBlah
 and see where it "might" have been published on a forum, a website, an email that is not Tor protected.. or even in your phone metadata (yes they can search this too)

so if you use the same address linked to other usernames or cellphone data they can get you, or atleast expand on searchable phrases to narrow down on you.

if you then put the funds from the drugs site withdrawal into a known exchange deposit address or an known amazon/retail deposit address. they can try seizing personal Identification from these companies.

the thing about bitcoin is that its your money and your address.. no one is forcing you for information linked to every address you use. so if you hide it well and not link your identity to it you can hide..

just like bank notes. there are not very many places that will ask you for ID so if you avoid using a banknote with a tainted serial number in a place that asks for your ID. no one will know.