I think SE deserves some of the blame for this; many duties have mechanics that are too punishing or hard to learn for new people and groups that are made up of mostly new people will be destined to wipe. If it's is a new duty with hard mechanics, then the person who solo DFs into it has unreasonable expectations (not to have new people) but if it's an older duty that is frequently cleared in DF because most of the community understands the mechanics at that point, then you can't really blame the person for wanting to leave and try their luck with another DF group. Many new players simply do not understand/accept that their lack of knowledge will doom everyone else. I'd suggest they watch a video but every time that can of worms gets opened, the baddies that forget this is a team game go nuts.
Well I didn't say "no penalties," I said "no penalty timers;" there are other ways to prevent players fishing for specific duties. For example, have roulette bonuses disappear after entering a duty rather than on completion. This idea isn't perfect (it's just a quick brainstorm anyway), but I think the possible consequences (like losing a bonus due to a votekick or DC) are less of a downside than disabling one's ability to play at all.
We pay to play the game in order to have fun but penalty timers say that if we're not having fun, we ought not to leave, and if we do leave, then we can't play/have fun for 30 more minutes. At the extreme end of the scale, where this occurs frequently and/or the penalty timer increases, people will just quit paying/playing the game altogether. Some probably already have. I know any time I am verbally abused, leave a party, and then to add insult to injury, I am penalized for it, I think about playing something with rules that make a bit more sense.
Forcing: power to influence, affect, or control. A penalty timer exists precisely to influence player behavior. Sure, a person can leave a duty, disobey a rule or law, stand up to a bully, etc. People don't always do what they want to do because the external influences are too strong (i.e. forcing them). People shouldn't always do what they want to do (but that's another story).
However, since FFXIV is a game people should mostly get to do what they want to do (within reason). We can debate whether or not players should get to leave a duty without penalty but since it's just a matter of opinion, neither of us can be "wrong." But there are right or wrong business decisions for SE to make and I don't think it's out of the realm of possibility that it would make for a better game to do away with penalty timers. I'm not personally affected by this very much but when I am, it really annoys me ("Why do I have to take a penalty because others were jerks to me?").
Whenever I go play another game for a 30 min period of time that I can't play FFXIV, I'm more likely to just continue playing that other game. That seems like the wrong type of influence for SE to exert.