Teribus.

Capitalism is an economic theory.

A Capitalist however, whilst being:

1. a person who has capital, esp. extensive capital, invested in business enterprises.
2. An investor of capital in business, especially one having a major financial interest in an important enterprise.
3. a person who invests capital in a business (especially a large business).

(the same definition from different sources)

or simply a person of great wealth,

can also be,

1. a conservative advocate of capitalism (noun)
2. favoring or practicing capitalism [syn: capitalistic] [ant: socialist] (adjective)

... note the antonym ...

3. A supporter of capitalism.
4. an advocate of capitalism.

A supporter of capitalism will as a matter of course need to justify it in the context of politics and the political issues that surround it.

Any argument advanced in that context can be said to be a political argument.

A self proclaimed capitalist can therefore be said to be representative of a political ideology.