Agents, a well known one once told me, are facilitators. I agree that it can appear obstacles are thrown up now and again to push people towards bypassing regular channels and enlisting an agent. But toeing the line in Thailand would get you nowhere. I feel for those who are older, have disability etc, standing in long lines in the sun and being herded about is just impossible for them.....
I suspect immigration would be even more crowded and confused if agents weren't applying some semblance of organization. Remember Chiangmai some years back.. didn't people have to arrive at 5am to stand a chance... and be waiting in a crowd? Without help, many will just risk overstay!