Since obviously the OP's friend is the only person bizarre enough to think it's not a career, and we here all agree, I thought it might be interesting to talk instead about whether it's a "profession".
en.wikipedia.org/wiki/Profession looks like a good basis for such a discussion. Of particular note:
"A profession is a vocation founded upon specialized educational training, the purpose of which is to supply disinterested objective counsel and service to others, for a direct and definite compensation, wholly apart from expectation of other business gain."
"A profession arises when any trade or occupation transforms itself through "the development of formal qualifications based upon education, apprenticeship, and examinations, the emergence of regulatory bodies with powers to admit and discipline members, and some degree of monopoly rights."
So far so good IMO, I'd say marketing meets those criteria.
"Typically, individuals are required by law to be qualified by a local professional body before they are permitted to practice in that profession."
This, I think, is where it starts to trip up. Since you can legally "do marketing" without any qualifications, even though most marketers do acquire such qualifications, that's a strong strike against it being a profession.
"Professions enjoy a high social status, regard and esteem conferred upon them by society."
Okay, never mind then ;) (joooooke, marketers!)