There are a lot of challenges we have to overcome to travel to the stars, but this is certainly not one of them.
What weapon system would be "good enough" anyway? A potential other civilization could be completely primitive, or it could have faster-than-light travel for millions of years by now.
To me it seems entirely absurd to consider this as one of the major problems.
Maybe not weapons development. But doesn't the whole problem bear some thought?
The strategic problem postulated here would be defending planets, presumably from collisions with masses moving faster than light. Warheads aren't more than an afterthought, right? I don't see how anyone spots the inbound attack, never mind puts enough energy on it to change its vector.
Which suggests that the only balance comes from deterrence. But how would any actor know who originated such an attack? Or where they come from?
If that's the battlespace, then "here I am!" might not be a great opening move. And given the importance of information in this battlespace, deliberately avoiding knowledge of who lives where might be the only way of signalling you won't be a problem.
It's all speculation but it's one plausible scenario. Maybe we should have this figured out before we start wandering around.
Of course it may happen that becoming more visible in the universe would provoke impossible to defeat enemies against us. But the argument for this is purely hypothetical and one could similarly make an argument that sitting around on our rock and not expanding could end in us being wiped out (cf.: Every primitive culture on Earth ever wiped out by explorers/settlers).
It seems impossible to decide which way is safer with our current information, so I'm for expanding/exploring till we know more.
To me it seems entirely absurd to consider this as one of the major problems.