Since the money and resources to explore space or solve the problems that human already facing on Earth are very limited; it should be spend reasonably. In reality, people have different reasons that supporting justify their arguments and have their valid reasons.
While in space, there is no limit of when to stop exploring as human still do not have the technology to know the scope of the place we called space and we also do not know that whether these actions can be useful in the future or not, so some people might think it is absurd ideas to spend money on something that may lead to beneficial as finding new places for human to live in the future or just spend billions of dollars on something that might found fascinating, but useless in practical.
On the other hand, we know for certain that these money can help to find the best solutions of the problems that we are currently facing or even the the rate of possibility of problems that we might get in future. There are a lot of problems that exist globally like hunger, flooding and etc. We try to solve it, but because of the obstacle which is the core problem of overpopulation that leads to over concumption are pretty difficult to solve. Every small problems have the bigger problems inside it that leads to the current problems. It is like a loop that will happen again and again, no matter how much we solve the fixed factors, we cannot solve the variable factors.
But what if the money that we spend on improve the circumstances on Earth can only slow the problems, not solving and it leads to disasters after disasters. And we need to find a new home, but again if we cannot find it. There is no best answer in this arguments as we do not know the scope of exploring the space and how much it can be benefit us. We also do not know the scope of problems that we will face. It is truly a sad fact that this situation is a dilemma, that no human can solve it fairly in this era.