I'm going to sound like a broken record after posters like Interest Compound(great post BTW!).
100% stocks is practical for a very slim population of people. This population is so small I would rather just say they don't even exist for the betterment of the rest of the population because so many investors 'think' they are in this crowd, and they are not. There is also a very big difference between being comfortable with 100% stocks when you are working VS retired. It is easy to say you are comfortable with a big crash right now when the market has been up for years and when you have an income. Think back to what a big crash feels like. It isn't just your portfolio dropping. It is the new media running 24/7 doom and gloom, it is articles predicting DOW 5,000, it's companies going bankrupt, it's layoffs, it's articles about how this crash is like the great depression again, articles about how this time is different and it will be even worse than the great depression. People will be buying gold again. People who are in your normal investing support group who were also 100% stocks will be telling you they missed the crash and are in cash right now(BTW, they lied, they sold after it dropped). People will make you question whether a 100% stock portfolio was a good idea in the first place, and amplify this feeling when you are actually spending from the portfolio.
People who are comfortable being 100% stocks are the forever bulls. They see every crash as a buying oppurtunity. They don't see down 70%. They see 70% off sale. They pray for crashes so they can buy more shares. They are mad at the market for being so high right now. Why can't it just go down a little so their next contribution can buy more shares? I can tell you most of the people who fit in this crowd wouldn't buy a high dividend fund with the mindset that the dividend will help them keep their cool in a crash. They wouldn't need that reassurance. What if your dividends stop or they start trending so low the dividends alone can't sustain you? Look up VYM from 2007 to 2009. Dividend income was lower in 08 than 07.
60/40 VS 100% stock. Average return since 1926: 8.8 VS 10.2%. Historical worst year: -26.5 VS -43%. For 1.4% higher annual return you are increasing the worst year downside by 62%! One crash. If you make the wrong move(sell) in one crash with a 100% stock portfolio your FIRE plans are done. From the peak in 07 to the bottom in 09 a pure stock portfolio was down 55%. If that happens in the first year your 4% SWR just turned into an 8% not safe WR. Even if you stay in... will the market recover fast enough? One year of low returns and your 8% WR is now a 10% WR... then 12%... how long can you handle this? Years? If you have even an ounce of doubt today imagine how you will feel when your livelihood depends on this.
One potential safety net using a 4% SWR: 20X expenses in stocks, 5X expenses in bonds, an 80/20. As the portfolio grows keep 5X expenses in bonds. You could easily end up 90/10 over time. If the market crashes, spend from the bonds to leave the stocks alone. When the market starts to recover decide based on how you felt in the last crash whether you want to add the bonds back. The idea is that the bonds let you get through your first crash, whether that is 1 year away or 5 years away, so that you don't have to worry about sequence of return risk in the first few years. If you make it through that then a 100% stock portfolio has a very high success rate. There have also been studies that back up being a bit more conservative right before and after retirement, and then becoming more aggressive over time. PS, 80/20 has averaged 9.6% returns so you are giving up very little return to do this for the first few years. (Not saying I'm doing this. I just thought it was a good 'fail safe' on your way to 100% stocks in retirement.)