@They fail to explain one thing
"A little law concerning the conservation of energy tell us that either way we will need the same amount of energy whether it comes from petrol or electricity"
Er.. kind of. You aren't taking efficiency into account though are you? ICEs are wildly inefficient... Far less efficient than the charging of a battery from mains, which discharges into a motor - even taking power loss through the National grid into account.
You are making the assumption that 1MW of power produced at a coal fired power station, and delivered to your home / filling station via the national grid produces the same amount of CO2 as, say 20 Fossil fueled cars producing 40KW of power. This assumption is utterly ridiculous.
"...and since we produce electricity using fossil fuel..."
Correction: "we CURRENTLY produce MOST OF OUR electricity using fossil fuels."
Electricity can be generated from dozens, if not hundreds of different sources, and while the majority of it is currently produced in gas, or coal fired stations, this can change, and is changing - albeit quite slowly.
Wind, Tidal, Wave, Nuclear, Solar, Geo-Thermal and a few others are already being put into use all over the world. Hell, if we wanted it badly enough we could chuck a satellite up in orbit to convert solar energy to microwave and beam it down to earth.
You also aren't taking into account micro-generation - i.e. solar, wind and hydro in the home... Almost anyone can get solar PV panels put on their roof(all you need is a roof within 45Degrees of south), or a wind turbine in their garden (if they have one) - several rural areas even have hydro-power from rivers & streams - essentially free (post-setup costs, of course) energy with 0 emissions.
YES there are issues with the manufacture of Lithium Ion batteries and the emissions caused during manufacture.
YES there will be a greater load on the national grid (But they are going to have plenty of notice of the changes and should adapt)
YES there are issues for people who don't have garages or some other means of charging their vehicles.
NO it isn't perfect, but there isn't going to be a perfect solution, certainly not around the corner anyway.
Plug-In hybrids are just a stepping stone - they have the ability to be 100% electric and POTENTIALLY 0% CO2 emissions for 90-95% of their use (i.e. commuting to work) while being able to fall back on petrol (or preferably diesel) for the odd longer journey.