Today you can read a lot about ethical and unethical doing and specially about companies that do act unethically or unfair. For a public person it's not always easy to determine if such accusations are righteous or not. My question: Is it unethical to invest in shares of companies, whose reputations are not that good because they are accused of repression of employees or groups (or supporting such repression), exploitation of nature and human, etc.?

An interesting and very timely question. It seems to me that it breaks down into several parts. First, we need to ignore the problem that what one person believes is unethical corporate behaviour another believes is appropriate competitive behaviour. For example, much of the current trend in ethical investing stems from religious groups, many of whom refuse to invest in companies that produce alcohol, as well as those that produce and sell arms to oppressive regimes. Many would for good reasons count the latter as a more important oversight than the latter. Let us assume that we are all agreed that behaviour X (using your example, treating the workforce in some particular way) is unethical. Second, your question assumes that if a company were in fact guilty of X, then that alone would preclude investment in it. However, corporate activities are complex; one might be inclined to take a holistic view of their activities and ignore one thing because of activities you feel are...