Putting aside the environmental argument (even if it's the most important one): The economics of fossil fuel, generally, and tight oil in particular, absolutely suck.
Tight oil is already heavily leveraged. Four letters to think about: EROI -- energy returned on energy invested. In other words, with shale and tar sands, you have to USE energy-- much, much more energy-- to extract oil. It's just not that profitable (except for oil executives, obviously) and that's just one of the reasons it's so heavily subsidized.
That's a desperately inefficient use of resources. It's front-loading our consumption, ensuring that we use more barrels of oil to generate the same amount of energy. and guaranteeing that we will have less of it later, later in the collapse. That's a real problem, because we will need some fossil fuel, in some capacity, for a long time, and oil is a FINITE resource. We'll need it for critical infrastructure while we transition to way, WAY lower consumption and alternative energy sources.