Brewer, what alternative do you have for tankers to transport petro? The incidents that have occurred on US ships are human factor incidents and the operators with which I am familiar have addressed them. Those that were engineering in nature are being addresses by the Coast Guard.
A better investment approach, IMHO, is to consider the business risks and not to hold more than you can aford to lose (just like a bond). If enviornmental actions are a factor, buy US or, perhaps Norwegian, shipping companies. If employee relations are a factor I could ask around (I know one US firm I wouldn't choose).
The same issue arises with pipe lines. Pipe lines have risks, but the alternative is transport on the highway. Which is the lesser?
Whether or not investment in other industries is likely to be more profitable is a different issue.