The question at hand isn't whether your opinion honestly matters on the internet or not. The real question is "are you willing to put effort and energy into making your opinion heard"? It's very debatable as to whether anyone's opinion honestly matters, of course, as some people's opinions can be rather ignorant or venemous (both rather unpleasant things to read). But if you actually put work into trying to make your opinions heard, you are displaying an initiative for self-improvement (from any comments people may leave regarding your opinions (and by that, I mean intelligent criticism, not "OMG U SUK U FAGET")) and from that may end up improving yourself as a writer.

Of course, you could just be displaying an ego (Hey! I have my own webspace and you don't! Ha ha!), but hey, everyone has one.