For example - brokerages keep you from trading on margin unless you have x money and y experience trading on margin and/or options.
You CANNOT invest into SpaceX (not pioneering SpaceX here, just an example) unless you are an accredited investor, that is, if you aren't RICH. Google does though.
These are serious disadvantages.
The real question is whether you want to be babied and coddled by people in power.
Edit: Deleted "controversial" topic sentence.