But since Rogan does not object even the most outrageous arguments, for someone who knows nothing about a field, this can seem pretty plausible - that guy’s an expert after all.

Somehow I highly, highly doubt that your average typical 20 year old is going to seriously think that a guy talking about spooky aliens in area 51 is an expert, let alone accept what they say as true. Even in the extremely rare off chance that somebody does believe someone like Bob Lazar, they're literally a 10 second Google search from figuring out that he's a nut. Again, the premises that you give don't exist anywhere but in your mind. If you can figure out that Bob Lazar is a nut and I can figure out he's a not, then so can anybody else.

… and then takes every of their arguments at face value. If he’d be even a tiny bit of a journalist, he would ask actual questions and maybe even contextualize some of their arguments.

He's not a journalist... I'm not sure why you're having difficulty grasping this. His podcast is not about fact checking his guests or grilling them with hard questions or making them uncomfortable. His podcast is literally about having interesting conversations with interesting people. Like normal, lighthearted, organic conversations.

He legitimizes dangerous people, his stupidity is not a persona - he is actually stupid. That’s extremely problematic.

No he doesn't. I'm sure you listen to a few podcasts and watch a few TV talks shows, do you legitimize every guest that comes on them? If you don't then it's the same for others, and if you do really legitimize every person you see on the shows you consume then your statement applies more to you than to him.

As a contrast: In Germany there’s a podcast called Jung&Naiv (young & naive)

Again, Joe Rogan's podcast is not meant to be political or journalistic or anything of that nature. It's meant to be interesting and entertaining. You can't compare it to some political podcast in Germany because they're not even the same thing. It's like questioning why Family Guy isn't like Painting with Bob Ross. Like yes, they're both podcasts, but they do completely different things, serve different audiences, and have different intentions behind them.