Is the use of torrent sites to download TV shows wrong? Or is it OK on the grounds that it makes a stand against the invasive advertising techniques used on television?

The "invasive advertising techniques used on television" would make torrenting TV shows justifiable only if we had some sort of right to watch these shows without advertising. But I don't think we have such a right. TV shows are produced or purchased by networks at some cost, and they recoup that cost (and earn a profit) by selling time for advertisements. That you dislike or even disapprove of these advertisements doesn't give you the right to make use of their products in ways that the networks oppose. They own the shows, and thus they can determine the conditions under which they are broadcast. If you want to take a stand against advertising, don't watch the TV shows at all. Or just buy them on DVD. That way you can pay for them without submitting yourself to those invasive advertising techniques.

Do very large corporations have a duty to be ethical and to involve themselves in charity? Is the duty of a pharmaceutical company which makes life-saving drugs more than the duty of a company which produces 'unnecessary' items, like a company that produces sparkly party hats, even if both are the same size, make the same profit, etc?

This is an interesting question. Actually, I think you're asking two different questions here: (1) Do corporations have a duty to behave in an ethical manner, and (2) Does ethical behavior necessarily involve charity? The answer to the first question is certainly that corporations do have a duty to behave ethically. They have duties, for instance, not to include false or misleadings statements in their advertisements, not to use harmful chemicals in their products (whether these products are life-saving drugs or sparkly party hats), not to contaminate the water supply, and so forth. The second question is more difficult. After all, ethical theorists disagree about whether and to what extent individuals have a positive duty to give to charity (or, more generally, to be beneficent). And even if you're convinced that individuals do have such a duty, that hardly settles the question of whether corporations have one as well. I tend to favor utilitarian or consequentialist moral theories. A...