There's nothing wrong in trading only Bitcoin mate. Any one can decide to stick to what flavors them the most, so long you know how to manage your investment risk. For me personally, like I said I don't put much efforts into altcoins as I have past experiences with them and the only way I made profits was through spot trading. Aside that, holding altcoins sometimes puts your funds a high potential risk and if one is not careful, might end up losing them in just one bear season. I remembered buying an altcoin back then, which was actually in profits for about 2 months then I decided to take the risk and hold longer, unfortunately I came back to meet that the project got rugged and coins had no value. So we just need to know what we are putting our money into.