I like to consider myself a fairly ethical person; that isn't to say that I get everything right the whole time, but instead that I try my best to constantly evaluate what is ethical and act upon it.

A common attitude I find goes along the following lines;

Even if you don't do X the rest of the world will; so you might as well do it anyway.

I think this is a pretty common opinion which stops people doing what they otherwise know to be the right thing and giving into the easier options.

I think this view is flawed. The best way I have ever seen it summarised is by the wonderful Peter Singer in "A Vegetarian Philosophy". Give it a read and see what you think;

Some defenders of a variant of the ancient Buddhist line may still want to argue that one chicken fewer sold makes no perceptible difference to the chicken producers, and therefore there can be nothing wrong with buying chicken. The division of moral responsibility in a situation of this kind does raise some interesting issues, but it is a fallacy to argue that a person can do wrong only by making a perceptible harm. The Oxford philosopher Jonathan Glover has explored the implications of this refusal to accept the divisibility of responsibility in an entertaining article called "It makes no difference whether or not I do it" [Proceedings of the Aristotelian Society, 1975).

Glover imagines that in a village, 100 people are about to eat lunch. Each has a bowl containing 100 beans. Suddenly, 100 hungry bandits swoop down on the village. Each bandit takes the contents of the bowl of one villager, eats it, and gallops off. Next week, the bandits plan to do it again, but one of their number is afflicted by doubts about whether it is right to steal from the poor. These doubts are set to rest by another of their number who proposes that each bandit, instead of eating the entire contents of the bowl of one villager, should take one bean from every villager's bowl. Since the loss of one bean cannot make a perceptible difference to any villager, no bandit will have harmed anyone. The bandits follow this plan, each taking a solitary bean from 100 bowls. The villagers are just as hungry as they were the previous week, but the bandits can all sleep well on their full stomachs, knowing that none of them has harmed anyone.

Glover's example shows the absurdity of denying that we are each responsible for a share of the harms we collectively cause, even if each of us makes no perceptible difference. McDonald's has a far bigger impact on the practices of the chicken, egg, and pig industries than any individual consumer; but McDonald's itself would be powerless if no one ate at its restaurants. Collectively, all consumers of animal products are responsible for the existence of the cruel practices involved in producing them. In the absence of special circumstances, a portion of this responsibility must be attributed to each purchaser.