If 0 is completely unrelated and 1 is absolutely related, then 0.3 is much closer to unrelated than it is to related. If you want to prove something to be related, you typically want a 95% correlation, which means that in your specific study, there is only a 5% likelihood that the results you have found were based on chance alone. With the 0.3 correlation, there is a 70% chance that your conclusion is based on chance alone. That means that it is almost as statistically unrelated as it can be. Actually, based on the numbers, there is a 70% chance that the correlation is completely unrelated. When you put it that way, you should probably drop the argument