Why is it a bad thing? Have you taken the time to talk to some of the women who appear in these ads? They may have a bigger problem with your labeling them as "advertising objects" than them appearing scantily-clad.
It's quite likely that the models in the ads have no objection to what's going on- clearly, they chose to get into the industry. But that's not really the point- there is such a thing as being aware of your environment, and the tech industry has started making real efforts to be more inclusive. If you don't pay attention to this kind of stuff you're going to get a backlash.
Are you saying that they simply made the wrong ad for their tech audience(easier to agree with for a moment) or that they made some huge moral blunder(more difficult to agree with, also the argument by the lady who started the conv).
But imagine, for instance, that she tweeted something similar to @playboy. She'd be very unlikely to get a positive response, or really any support from others. But the tech world is not Playboy, we're supposed to be an inclusive community that wants to encourage more women to be involved.
So I guess my answer is somewhere between your two options- they made a moral blunder in the context of the tech community.
In other words,
OK: that model is being used as an object for marketing clothing
Not OK: women are objects that are fun to look at
I can't really agree to the position that sexualized advertising is inherently sexist. But in the case of geek culture, there is a big heap of social context that has to be taken into account that makes it very touchy territory.