Inkscape 0.47 and later will support curve editing via Raph Levien’s vastly superior Spiro curves:

I round-tripped through FontForge when I drew the Seal of Rassilon for a recent t-shirt design, just so I could use spiros to do it:

Achieving nearly perfectly tangent and parallel curves using spiros is trivial, compared the the fragile finickiness of Béziers.