Robert Recorde invented $=$ in 1557 with a simple justification: no two things can be more equal than two parallel lines of the same length (chapter 1 tells this story, in the text on the signs of the operations). The sign caught on so well that today it does jobs Recorde never imagined. Look at these lines: $$3+4=7,\qquad 2x+1=7,\qquad (a+b)^2=a^2+2ab+b^2,$$$$f(x)=x^2,\qquad \tfrac12=\tfrac24.$$The sign is the same in all of them. What it says is not.