When working with vector graphics that need to be converted to raster you have to pay extra attention to two things: resolution of the rasterization and anti-aliasing.
In this example it seems your rasterization resolution is both too low and you do not have anti-aliasing enabled. If the software you are using does not offer anti-aliasing then the thing to do is to rasterize it at twice the needed ppi/dpi and then downsample it in a raster package (using a color format of RGB -- if you resize in B&W/Bitmap color mode then there will be no anti-aliasing created).
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