Well yeah, "renewable" in itself is only good in certain contexts, such as solar and wind energy.
When it comes to renewable biomass, which by definition is renewable too, it's not so friendly to the environment anymore. It consumes huge areas and destroys the rainforest to plant even more economically usable plants. Such as soy, cotton, ...
So i'd rather see huge amounts of underground oil being consumed, than the same amount of biomass out of the rainforest being consumed.
... well, in its defense, if it weren't subsidized, renewable plastics would indeed be cheaper, but only at the expense of huge areas of farmable land and the rainforest. So it's either "consume 300% of the planet's fertile land to produce plastics" or "subsidize oil".