This is a strawman or poorly explained. It is not explained to us how law enforcement has connected the onion friends to the mail provider, but that is not proof that law enforcement do not have evidence of such a connection. It is also not clear to us that the onion friends is not connected to the operation of the mail provider. The presence of a bank account in fact suggests otherwise; the funds in the bank account does indeed facilitate the operation of the mail provider.
Can anyone explain better?
Let’s switch out the entities and see what you think. An anonymous blog posts terror threats and links an email @gmail.com, the investigators discover that onion friends have a bank account supporting donations to google. So they raid onion friends.... does that seem justified?
If the onion friends had a donation page up to support a terrorist group, I think they should be monitored by security police and raided if there was a reason.
Your case when the bank supports google is not a cause since google is not a terrorist organisation.
In this case of the onion friends, the donations seems to have been going to donations to a anonymous mailer web site, and depending on what is done at that web site, raids could be justified or not. I think the "connection" has been established, which CCC would like to say there is none. Yet, in your own example, you seem to admit a connection, just not a cause for a raid.
CCC: "The mere presence of an e-mail address at a large free provider on a website has caused law enforcement authorities to deduce that a German association that helps raise funds for this provider must be connected to this website somehow."
This is a strawman. It is not shown by CCC that this is how law enforcement connected anyone to the website. In fact, CCC themselves admit the onion friends are financing the website.
CCC: "The Zwiebelfreunde association has a bank account to facilitate donations to riseup.net."
Financing a web site seems to me to be a valid reason to connect you to the web site. By now you need to argue semantics of what "connected" means in the law, and you are not in Kansas anymore.