I think people consider it, and the FIRECalc can take it into account. There are some big risks, especially the younger you are at retirement. (If you are 45, or 50 or 55 right now, or will be 55 or 60 when you start this plan, disregard the following)
Assume you may live to 90+ and you are 30 or 35 at retirement. You'd have almost 60 years, and 30 years until that SS benefit kicks in. I don't think people under 40 should rely on SS until they see where things are at age 50. Second, even if SS does exist exactly as it does now, your benefit is based on your highest earning 40 quarters. If you only work 10 years and some of those were entry level jobs, your benefit might be lower than you anticipate.
The 4% SWR is based on looking at any 30 years of market returns, not 60 years. The odds of a long depression/ big crash/ high inflation in any 60 years are higher, I'd think. If that happens right at the beginning, you might be in trouble running a deficit for the first 5 to 20 or 30 years. In some of the scenarios, at the end of 30 years the balance is 0, which is fine if you die, but not if you have another 30 years to live!
If you have a 10 year work history and then live on savings for 20 years, and then find you don't have enough cash due to SS changes, market conditions, life changes, etc, you are now 50, with no recent work experience, and very old educational credentials. It might be very difficult to find a job. This is true for any young retiree, but it is worse if as you say you plan to do NO work, and it's more likely if you are living above your income.