If the ex-politicians and current lobbyists were not being paid any money, no one would complain. The big issue here IMHO, is that they are paid well; hence, they are easy targets for,"..it ain't fair...they are using their previous network to make outrageous sums..." and so on and so on. In a word--envy is the basic underlying problem for the complaints.
In my humble experience, they often don't add any value. If it's a policy wonk like a Pat Moynihan or a Jack Kemp, that would be different.
You really feel like taking a shower after meeting with one of the former kind.