There is exploration and there is colonization, which to some degree are orthogonal and to some degree complementary to each other, but they are not the same thing. Manned missions to Mars would mostly be about colonization, though exploration would be a significant side benefit. Mars is by far the most promising candidate for colonization (with the potential for using local resources to enable an early level of significant self-sufficiency, increasing over time) which would help kickstart our capabilities in interplanetary spaceflight in general, both manned and unmanned.
