I thought it would be useful to look at the stories the EU told itself back in 2003 when they convinced themselves of the necessity of encouraging biofuels. The 2003 directive [Google HTML conversion of this PDF original] has 29 reasons why biofuels should  be promoted ("whereases"). Here they are in soundbite form:
1 The Göteborg European Council of June 2001 included biofuels in the EU's strategy for sustainable development
2 Fossil fuels are leading sources of CO2 emissions
3 Biomass could be a source of fuel
4 Transportation accounts for 30% of EU energy consumption (and increasing)
5 The Commission's white paper on Transport policy for 2010 expects CO2 emissions from transport to increase by 50% between 1990 and 2010, of which 84% is due to road transport, which uses 98% fossil fuels.
6 biofuels for transport can help meet Kyoto targets
7 biofuels for transport can reduce dependence on foreign sources of energy
8 biofuel blends can already be used by existing vehicles.
9 higher biofuel blends could be used in public transportation ("captive" fleets)
10 promoting biofuels will encourage biomass use and so research into further applications
11 hydrogen research should be promoted alongside biofuels [???]
12 biodiesel from vegetable oils exists
13 biofuels should not be allowed to negatively impinge on emissions standards
14 biofuels should not negatively affect engine performance
15 sustainable biofuels would allow sustainable rural development under the CAP
16 On 8 June 1998 the Council endorsed the Commissions strategy on renewable energy and asked for biofuels
17 The Commission's green paper on securty of energy supply calls for 20% alternative fuels by 2020
18 Biofuels need to be available and competitive [presumably this is a justification for subsidies?]
19 On 18 June 1998 the EP asked for 2% biofuels over 5 years
20 We don't know what the best way to promote biofuels is
21 National biofuels programmes should not infringe on the common market
22 Energy security, greenhouse gases, usable already, distribution savings [escept for the latter, isn't this just repeating othe points?]
23 The member states by themselves may not be able to achieve the 5% target by 2010, so the EU may act by itself [i.e., subsidiarity allows EU action in this case]
24 R+D in biofuels should be promoted [why? dunno]
25 the economic, environmental and social impact of an increase in biofuel use should be studied [presumably, as it reaches 5% by 2010, to decide where to go from there]
26 the regulatory framework should be flexible to react quickly to new technological [including agricultural] developments.
27 the regulatory framework should be developed quickly to ansure biofuels don't damage engines
28 [incoherent mess on] security of supply, environment, and publicity
29 [irrelevant EU legalese]
Who writes this stuff? This is a confused mess, but it basically boils down to:
1 reducing carbon emissions
2 reducing dependence on foreign oil and gas
3 not compromising on emission standards
4 not compromising on technical standards for engine performance
5 encouraging rural development under the CAP

Nothing is 'mere'. — Richard P. Feynman