Where I live there is no legal max. I carry 3"-4"... I find under 3" a bit small for many cutting tasks, even though they might work , they just are a hassle to do it well and easily, and frankly for me the point of carrying is to make things easier.
4" tends to be the upper limit since its tough to find folders over 4" that don't look "scary" and a 4" fixed is plenty large to carry discretely.
Finally I agree that people notice style before they notice size. Also people tend to notice blade mass more. A 3.5" slipjoint has a much smaller overall blade than sometyhing like a Zero Tolerance with a 3.5: blade because the depth of the blade is less than half, I also notice that the colour and scales are a big factor. Jigged bone, or MOP is less scary than, brown/tan/white micarta/G10 which is less scary than black or camo...
4" tends to be the upper limit since its tough to find folders over 4" that don't look "scary" and a 4" fixed is plenty large to carry discretely.
Finally I agree that people notice style before they notice size. Also people tend to notice blade mass more. A 3.5" slipjoint has a much smaller overall blade than sometyhing like a Zero Tolerance with a 3.5: blade because the depth of the blade is less than half, I also notice that the colour and scales are a big factor. Jigged bone, or MOP is less scary than, brown/tan/white micarta/G10 which is less scary than black or camo...