Is it ethical to work for a major corporation?

[Nikia]

I am interviewing next week for a poisition at a company that has plants world wide. It's products are sold worldwide too. They are predatory in buying smaller companies to gain more of a market share. Working for a large company would give me chance for advancement and actual training. I don't know if I would feel good about this though.
I already have a job at a small company, the type that this company would like to buy. I am not happy there though.