Not if you pick the right SWMBO... just saying.
Why do you need a thermometer for boiling water? It only boils at one temp and it's pretty apparent when it's reached that point, no?
And who said anything about a 27 gallon conical? I could easily do a 25 gallon batch and ferment in 2 Sankes, or do a 10 gallon batch and do it in one Sanke or 2 carboys (every brewer still has carboys...)
Best thing about brewing big is doing experimentation on finishing hops, yeast, oaking, fruiting, etc off a single batch. I recently brewed one large batch of porter and fermented with 2 different yeasts to see which I liked better, then I also did 5 gallons each of vanilla/oak/bourbon and 5 gallons of blueberry porter.
So I got 4 beers out of one brew day.
Honestly, the majority of reasons given here are hyperbole and not REAL reasons to not scale up. The equipment costs and the ability to use/consume vs liking variety are the most viable and common reasons. The rest seem to be mostly excuses.