Let's talk about English usage!
It would be better to say "not everything that is stupid is unconstitutional." "Everything that is stupid is not unconstitutional" can be read to mean that every stupid thing is constitutional, when plenty of stupid things are unconstitutional. I know there's some argument over whether this should actually be considered a usage error. The argument that it's not usually brings up Shakespeare's "All that glisters is not gold." Why didn't he write "Not all that glisters is gold"?
Here's a discussion of the usage dispute:
"All ... not" can... be condemned on the grounds of potential ambiguity. When I proposed the sentence "All the people who used the bathtub did not clean it afterwards" as ambiguous, many people vigorously disputed that it was ambiguous. But they were about evenly split on what it did mean!... "Not all the people who used the bathtub cleaned it afterwards" (or, if the other meaning is intended, "None of the people who used the bathtub cleaned it afterwards") is free of this ambiguity....So, forget about this particular language nicety, I'd say. I'm rather glad to myself, since I was personally needled for years by someone who was inordinately vigilant on this usage point.
Fowler quoted a correspondent who urged him to prescribe "not all", and commented: "This gentleman has logic on his side, logic has time on its side, and probably the only thing needed for his gratification is that he should live long enough."
Not every ambiguous phase is a usage error/every ambiguous phrase is not a usage error.