I'm sure some good UX could alleviate this. Maybe a spinning gear icon? Maybe a battery draining animation? Something to signify, 'this tab is doing some heavy lifting right now'.
It's actually a pretty rational response for someone who is only moderately aware of what is going on in their computer. If they are aware that malware and adware can cause unwanted changes on their computer, perhaps because they've been bitten before, then a new icon -- even one that is easily interpreted (which this one would not be) -- looks scary.