That's something to take up with your representative, because that's legal unfortunately (specifically: marketing similar products based on past purchases, and in my experience, the consumer market authority takes that definition rather broadly).
There's a second category of unwanted email where unsubscribing has as only effect that you'll get more spam because now they know that your email address is actively being read. The sender is a hacked server or a botnet, and no business is identifiable as sender. This type of illegal activity is what spam filters are designed to combat. You're not helping the designers by marking other email as spam: it muddles the data, causes legit senders trouble (like me, I don't have a newsletter but spam filters are so aggressive that personal messages sent from my server still regularly ends up in spam), and makes everyone's life harder.
There's a second category of unwanted email where unsubscribing has as only effect that you'll get more spam because now they know that your email address is actively being read. The sender is a hacked server or a botnet, and no business is identifiable as sender. This type of illegal activity is what spam filters are designed to combat. You're not helping the designers by marking other email as spam: it muddles the data, causes legit senders trouble (like me, I don't have a newsletter but spam filters are so aggressive that personal messages sent from my server still regularly ends up in spam), and makes everyone's life harder.