Lobbyists are paid to present a preferred opinion, pretty much by definition. If someone is a registered lobbyist then their opinion should be held with great suspicion when it is anything to do with the subject that they lobby on.
You don't have to register as a registered lobbyist in USA to present your own opinion. You have to register as a registered lobbyist to represent somebody's else opinion.
Now Michael Shellenberger may be one of the pro-bono lobbyists (admittedly I haven't yet found out either way), but this would put him in the minority of registered lobbyists in the USA.
I will note that he was at one point a paid lobbyist for Hugo Chavez. Was he presenting his own opinion then?