I'm not altogether sure that the governments are ending up colluding with the corporate sectors by giving charitable writeoffs. But, I agree that since governments are no longer taking the time to fund charities, thereby designating charities worthy to fund, the corporate sector are not giving to those charities most deserving. The corporations give to charities in their own interests. The smaller community based social agencies who do all the work with almost no financial resources do not come to anyone's attention. I believe that the growing reliance on the charitable sector is a bad trend.
Corporations can indeed set policy with their donations.
If we are to worry about tightening this than we have a lot of loop holes to tighten. I suggest that sound government policy and higher levels of corporate taxation are preferable to charity from corporations. Charities need regular funding to operate and they need to change so they reach everyone who needs help. I think Valpy is correct. In exchange for not having a welfare state, even a modified one, and having a low tax rate, corporations fund charities.