That thread is all over the place. The post you're linking to seems to imply that SMPs should give you more than a chance at med school. That's not what SMPs are for. The sole point of doing an SMP is to get into med school despite a weak undergrad performance. If you're concerned that an SMP won't be helpful to you, in case you don't end up in med school, then definitely don't do an SMP.
If your GPA is fine, then there's no point in doing an SMP. People with fine GPAs who want to do regular grad work aren't hurting their med school chances by doing regular grad work.
If your GPA is not fine, an SMP is something you can do about it. People with not-fine GPAs only get into med school by doing ridiculous expensive things...that have no value outside the pursuit of med school. That 2nd bachelors? That 3rd MCAT retake? That SMP? All that money from multiple app years? None of it is an investment in a career...unless you get into med school.
If you screw up in an SMP, you don't get your year or your $50k back, nor do you have a resume asset for doing something other than med school. If you're lucky, potential employers won't know what an MSBS is and they won't say "oh, you didn't get into med school?"
A whole lot of people who do fine in an SMP end up in med school. And some people, who are not up to the extreme rigor of the coursework, don't do fine, and don't end up in med school. Be smart: figure out before you start an SMP whether you can get A's in hard classes, and make sure you really really really really really want to go to med school. Take care of those 2 things, and you'll figure it out along with your classmates. Surf in on denial and you're in for a very bad time.
Best of luck to you.