I do think that marketing research and public opinion polling should only take place online. The reason for this is because, compared to phone polls or polling by question in person, is that people are brutally honest and will say what they actually feel and think. It's the only true way.
There's no reason why public opinion polls and marketing research have to be exclusively online. I've participated in marketing research conducted at local malls, when someone with a clipboard approaches me and asks questions. There's nothing wrong with that. I would like to see research and opinion polls by telephone stopped, though. People who want to participate in that can sign up for some list, but the rest of us should be left alone.
Marketing research functions in two ways. It identifies key characteristics and attributes of a product or service through individual interviews or group discussions (qualitative research).It takes place in many modes and in many places: Personal interviews, surveys within stores or other venues, focus groups at research facilities, surveys executed by telephone, mail.
No, marketing research and public opinion polling should not take place online only. When research and polling is conducted, they need a fair random sampling. If these were restricted to online only, they would not be getting a good cross section of the public. There are many people yet who do not use the Internet.
No, marketing research and public opinion polling should not only take place online, because someone might give a different answer talking to a person live or on the phone than they would give on the internet. Most people are not bothered by the occasional phone survey. Other methods besides internet are generally acceptable.