I don't see any Stoic practice as problematic or risky, but I would advise to engage in extreme versions of the negative visualization exercise only if you are an advanced practitioner. The negative visualization is a meditation during which you visualize, slowly and deliberately, something bad or discomforting happening to you.

... it is because one can build a compelling set of arguments - informed by science and thoroughly compatible with it - that to believe in anything despite the complete lack of evidence is, in fact, irrational.

I can't speak for others, but I find the fundamental idea that a life worth living is one during which one strives every day to become a better person to be compelling.

The Stoics thought that a fundamental insight into human life is that some things are up to us and others are not, the famous dichotomy of control. Up to us are our judgments, decisions, and actions; everything else is not up to us, because it is influenced by external factors.

I believe Stoicism can help anyone who takes it seriously and begins to practice it. It will help them flourish because it will provide them with a compass for navigating life, a general, flexible, framework to set priorities, and a set of techniques to achieve serenity and equanimity.

There are clearly people for whom Stoicism immediately "clicks," it comes natural, and others for whom it doesn't. Then again, Stoicism isn't the only positive philosophy of life. Buddhism is an excellent alternative, if it speaks more clearly to one's personality or cultural background.

The downside of skepticism: it can easily turn into an arrogant position of a priori rejection of any new phenomenon or idea, a position that is as lacking in critical thinking as the one of the true believer, and that simply does not help either science or the public at large.