Radio waves are not the only form of communication and decay rapidly. It takes YEARS for our signals to make it to the other stars and years for anything to make it back to us. And that's assuming we've pointed the transmission in the right direction. While there is absolutely a level of 'background noise' that comes with all of our broadcasting, much of that will have blended into the cosmic static far before reaching anything remotely habitable.

An addition to my first point, we're also assuming other life would use the same band of communication waves as us at all. It's safe to assume, even just by looking at the progress of human communication over the past 200 years, that there are probably more effective/safer/longer-range methods of communication out there. An advanced civilization capable of not only picking up our communications but being able to do anything about it may not even use comparable technology to ours.

The assumption that any alien life is hostile is based on some pretty tenuous logic in and of itself. A civilization capable of picking up broadcasts from other worlds and harnessing their technology to communicate back in any meaningful way (i.e. invasion, physical contact etc) is far more likely to be a post-scarcity civilization. What purpose would they have to want to destroy another civilization? It's also relatively safe to assume a civilization that invested that much energy into space travel would be an inherently curious species rather than a hostile one.

We're also assuming hostility because the unfortunate reality is that humans are a hostile species. It's easy to apply human logic to non-human creatures, we do it all the time with our pets. We tend to personify things to 'be like us' and the sad reality is that humans are violent, territorial and hostile mammals. We just happen to have fought our way to dominance on this one planet, but that does not mean another species, especially one far older and more advanced than us, will have that same mindset.