On the other hand, no one ever increased sausage sales by giving out tours of the sausage factory.

Maher's vision of what happens in an open convention rests on a very lofty idea of what would happen at the convention. A notion that the convention will be a high-minded, vigorous, and most of all entertaining competition where candidates are evaluated on their strengths and ideas and policy platforms and the like. Which would be lovely, and might indeed improve the Democratic brand and entice people to the party.

The flip side, though, is that an open convention might instead be a grubby, venal (twice in two posts!), cynical, nasty, dispiriting affair filled with things that will repulse voters. Deal-making, trading support for votes or positions or clearing out "lanes" in future elections for favored allies of delegates. Bitter accusations of racism, sexism, classism, elitism - vile rhetoric and mudslinging. True believers who think that their issue (climate change, Palestine, voting rights, what have you) is too important to be bound by the rules, and engage in disruptive and/or disgusting behavior that normies will recoil from. Where the only respite from the unpleasantness could be the tedium of endless delegate polling as the body tries to grind down from potentially a score of candidates to get to a nominee.

An entire building full of political flacks, hacks, and diehard partisans locked in a room screaming all the quiet parts out loud to each other in a naked free-for-all seeking power within the party and the country - not in a smoke-filled back room, but out in the open where everyone's got a cell phone and a social media account.

Bill Maher makes his living off of politically-leaning comedy content, so even that second possibility would be fantastic for him. Whether that results in anything good for the Democrats or their eventual nominee is another thing entirely.