Yes, but it makes it harder for the hacker. You'd be practically handing it to them on a silver plate.
Your understanding of the "hacker" mentality is somewhat misinformed. For starters it makes little difference to them if they have the source, or reverse engineer the binary. Secondly, they like a challenge - they don't want it on a silver platter, no bragging rights. Open-source software can be improved or abused, in the case of games it is more likely to be abused.
Based on what? Here are the facts: Almost every single closed source game has been cracked. Open source games, not so much. Explain how you, based on that information, conclude that open source software is more likely to be abused? Don't underestimate the week-end coder, some of the best coders are self-taught.
Sure. But if he can produce a better game in a fraction of the time, doesn't it seem reasonable that he should be the one making money, not you? If you've written a really good game you're likely to make some money out of it, but if it's open-source you're probably not going to make any money at all.
Why not?