I've said this before, but apparently it's time to say it again.
When I'm asked for an informational interview, I'll generally explain that my workload usually prohibits that but that I'd be happy to answer the person's questions by email.
The person is then never heard from again.
This tells me: (a) The person didn't actually want an informational interview and was hoping to turn it into a job interview without my consent, and/or (b) the person wouldn't have had any plan had I agreed to meet, and it would have wasted my time. Oh, and perhaps also (c): The person is randomly asking for people's time without a real need or desire for it because they read somewhere that informational interviews will help them in their career, and thus isn't very considerate.
If you're asking for an informational interview, you need to have a plan before you make the request. And if once you get a response, you realize that you're without a plan, you need to come up with one. Otherwise you end up making a pretty bad impression, and those are hard to overcome.