There is of course some middle ground here... One being running an ad-hoc campaign in a pre-existing campaign world. This gives the DM a vast source of material but is not as confining as running published adventures.
Then of course you can take any Published adventure and set it in your home brew campaign setting. Change some names and locations and you just spiced up your setting on the sweaty backs of professional writers.
Personally I very rarely use published adventures, I find they do not accomodate the free will of some of my crazy players who would sometimes rather follow thier own motivations rather than some contrived situation.
I have been in some Homebrews ranging from quite good to awful. The thing that mostly irks me about being a player in homebrews is the lack of perspective my character has... no history, limited geographical knowledge and so on. Unless someone has been very thourough and can present that material in a well written thoughtful manner I feel like I am being told what I know about the world to often... such as
>DM - A man screams here they come the lords of Gharion
>player - Do I know who they are?
>DM - Yes they are famous battlelords you should be quite afraid
The Flip side of this is as a DM players may know more about an existing campaign setting that I would like them too. If your players are the least bit sly they can use this knowledge without drawing to much attention to it or even do it without thinking about it.
I subconsciously recognized a DM I was playing with was using the maps from the Slavers series and kept finding my way though thinking I had been there before in the campaign but just recognized map clues.
Oh somewhere in there I had a point... Homebrews not always bad, pre-made adventures not always good.
carry on!
At the risk of starting a flame war...
I think your advice has less to do with the inherent 'dangers' of homebrew campaigns and more to do with the weaknesses of specific DMs you've played with.
In my opinion, a good DM tries to keep their campaign (whether homebrew or not) a place that the players enjoy. If you can see players are bored with the world or the adventure - you quickly take steps to fix it. If that means allowing them to step through a portal into Ravenloft because they hate "Mysuperworld"... so be it. Most good DMs talk to their players and actively solicit feedback to make sure they are enjoying the experience. I don't know any DMs that I respect who are so enamored with their world that they don't care about their players' reaction to it.
And the players have a responsibility as well. As a player, if you aren't enjoying the DM's world, speak up. Don't just grin and bear it until the campaign ends hoping the next one will be in a pre-fab world. You owe it to yourself and the DM to be honest about the play experience. Besides, if you don't speak up, the DM may assume you enjoyed the world and base another campaign in the same world.
Personally, when I was a player, I did tell my DMs about the stuff I liked and didn't enjoy in their worlds. What they did with the information was up to them... But I would never continue playing in a campaign that was less pleasant than a trip to the dentist.