SEO is not a career unto itself, but rather a facet of other jobs, such as copywriting, web design, producing, development and online marketing. The only kind of pure SEO job is an SEO consultant, but to be an SEO consultant you need actionable knowledge about all of the above fields.
SEO has proved to be yet another new aspect that practitioners of the above-mentioned careers have had to 'either learn or die'. It is now a fundamental part of creating marketing materials for the internet.
So a pro is that if you want to work in any of the above fields you need to understand how keywords and their placement affect the ability of users to find your business online.
A con is that SEO tactics are constantly changing. Some of the tactics that worked in the past are actually detrimental today, such as link farm backlinks, same-server backlinks and too many low-authority backlinks in general. You've got to stay informed, measure your results and contantly try new tactics.
A pro is that it is very rewarding in that you actually get to see your results in measurable terms. Pre-Internet marketing was mostly hunch and experience, because the only real metric you got at the end of the period was a sales figure. There were very few ways to say that this ad or that brochure produced results.
A con is that everybody and his brother thinks he can 'do' SEO. As a result, there is a lot of competition for SEO copywriting, etc, and there are so many hacks that many businesses don't trust a lot of SEO 'experts'.
A pro is that everybody and his brother thinks he can 'do' SEO, so there is a real value in a skillset that actually produces results, that can stand apart from the hacks.
A con is that in order to be an SEO consultant for a web site you need to have access to nearly every aspect of a web site, from the structure of the sitemap to the copywriting, to the graphic file names, to the marketing efforts of blogging and video posting. And it is a rare gig that gives you that much control. Sites have already been built with their non-SEO developers strategies, copywriters don't like being told to sacrifice their marketing prose by crowbarring in awkward keywords, and the marketers think they know enough about SEO to do it themselves.
Another fact or 'secret' that is both a pro and con is that the tricks are not that many, and they're not that secret. Any marketer or copywriter with intelligence and motivation can become SEO experts with some research, trial-and-error and careful tracking/reporting. Just like in IT, there are a lot of folks who try to make it sound more difficult or complicated than it really is.
A pro is that its fun, and as long as you're paying your bills, that's the most important metric of all.
Good luck, and have fun!
- Marketing Guru