How could you argue that it is unreasonable to expect Western businesses active in developing nations to adhere to the same ethical standards they use at home?
Western companies have many ways to rationalize unethical behavior in developing countries. One should note that these rationalizations are not always ethical reasons, but instead ways to justify or put a positive public spin on acts that are inherently unethical.
First, companies argue that they are conforming to all local laws. It is true that multinationals dumping toxic waste in developing companies, producing clothing in sweatshops, or buying from contractors who treat workers in an inhuman and unsafe fashion or use child labor is absolutely legal in some countries. Thus, one could argue that these practices are "reasonable"; although, whether one should consider practices "ethical" is a different matter.
Second, often in the case of corruption, multinationals argue that engaging in practices such as bribery is necessary because other companies do it, and it is necessary to create a level playing field. They might also argue that it is "reasonable" in terms of how local cultures work. However, simply saying that other people do it is not precisely an ethical justification, as under the same logic, it would be acceptable to commit murder or child abuse on the grounds that other people do it.
Finally, arguments are often made on the basis that the business of a corporation is to make profits for shareholders and that this obligation overrides all other considerations.
There are two main reasons for this.
First, the Western companies may want to act ethically but may be unable to do so. There are many developing countries in which practices that would be unethical in the West, such as bribery, are simply expected. It is unreasonable, one can argue, to expect companies not to “play by the rules” of the country they are in.
Second, it could be unreasonable to expect this due to competition. If there are many companies doing business in a given country and some are acting unethically, it is almost impossible for the rest to be ethical. If they were, they would be unable to compete with the unethical firms.