For me, it really comes down to how it's presented. Anime is much like other forms of film, in that there are "highbrow" and "lowbrow" examples, as well as a wide range of middle ground. When sexuality is included because human beings do on occasion indulge in sexual activity, and such activity currently serves the narrative, then I'm fine with it. When someone's holding down schoolgirl A, firing a high caliber rifle between the legs and breasts of schoolgirl B, causing schoolgirl A to emit strange orgasm-like exclamations, I'm not inclined to believe I'm watching high-brow entertainment. Now, having never really seen the show, and being pretty familiar with Zombie-related media, I'm going to assume I'll be told that the real draw of the show is the human interaction between survivors.
To that, I'll ask you "Why not just watch The Walking Dead, if breasts and the like aren't the draw?"
I don't have a problem with High School of the Dead (and similar anime/manga). Just because this particular example is not high-brow art neither means that it's not art, nor that it's bad art. If I were to tell you that it's bad art, that only means as much as you let it. Even me telling you that it's not a high-brow example of the genre is wholly my opinion.
I understand why you watch anime with these elements in them. I understand what it's like to be asked why you don't just watch porn. We don't really get a say in what the artists do with their series,and there's usually something else keeping us watching. I'm right there with you. What I don't get is why the artists bother with these elements, or why they get so much screen time. If the artist wants to draw large-busted women getting eaten by zombies, more power to him. If you want to watch a good zombie drama, I can get behind that. Hell, if you're looking for some zombie-on-schoolgirl action, who am I to judge with MY google history? What baffles me is what drives the artist to take his zombie drama, add tons of large-breasted women, focus every camera angle for maximum cleavage and upskirt action, and then stop short of them all whipping out the goods and having an orgy. What drives them into that gray area? It's not that the anime is distract-ing, it's that the anime feels distract-ed. It's as if the animator was in the middle of drawing a serious character drama, when he's overcome with lust and starts doodling large-busted women all over his paper. Maybe I like peas OR mashed potatoes, and here this guy is mixing it all together and calling it stew. I'm here for some peas; Or, if I'm feeling frisky, some mashed potatoes. When I'm watching stuff like High School of the Dead, I get ticked sometimes because the breasts break up the interesting character drama, and when I'm frisky the character drama drones on and on when I'm just fast-forwarding to the part where everyone gets naked and a bunch of voice actors are paid to "make sex noises, or something".
What really irks me is that the guy in tippy2k2's clip missed a whole crowd of shambling zombies, despite having good enough aim to fire between the legs and breasts of a moving target. He fires like five times, it's both a miracle that he missed his comrade that many times and completely baffling that he didn't even so much as clip a zombie in the shoulder. There's a whole crowd to choose from, and he finds the one tiny patch of open air through which he can miss. Unbelievable, even in the show's own context.