When creating campaing activities you can choose different channels.
Fx E-mail, Letter.
The field "Send Marketing Materials" on lead, account and contact records are respected.
This is fine, but fx Phone and Appointment and in some cases Letter should be possible to create even if this property is "Do not send".
I would suggest a field on the create campaign activity dialog asking the user to "Ignore send marketing material setting" default NO.
Because often we still need to be able to contact the customer by phone or direct mails.