Abramovitch over at the CBC forum thinks Harpers sports tax credit plan isn't any good because it's not inclusive enough. The plan is flawed for several reason, but a lack of inclusion is not one of them. For Marcie, all government tax plans and programs should be measured against the interests of those who earn LESS than the basic personal exemption every year.
Also, a significant portion of the population does not pay taxes. These Canadians' incomes may be so low that they don't need to use tax credits beyond the basic exception, and thus would not have their income taxed at all. Or, because they have enough tax credits already available, they would be paying no taxes. A new tax credit would not make any difference to the taxes they pay, and so would be of no benefit.
You can check out Marcie's othere thoughts over here.