Thing with taking humans to Mars is that these humans need to be confined in a small space for quite a while. Messages to Earth take longer and longer, so that takes phoning home on a whim out of the picture. On top of that, vacuum packed food even has a certain amount of time it can be kept. Also, drinking your own pee is not particularly a nice prospect, but a requirement on such missions.
These issues are all very minor. Submarines are cramped and people can remain incommunicado for months. Messages to Earth is essentially just means one will be relying on email equivalent. And vacuum packed food can keep for years. Drinking water that is reclaimed from pee isn't fun, but isn't a big deal.
What if there's a mechanical problem somewhere? Sorry, you can't quickly ask for a replacement part from Earth, and you still need to poop and piss. So you need to carry all of those parts along as well. Don't forget about the human body deteriorating in various ways, simply because there's almost no gravity.
Mechanical problems are a big issue. That's why for example even today submarines carry some replacement parts, and why big surface ships historically had machine shops. Some things will need to be carried. But others may need to be ready to be made on site. That's why there's now a 3D printer on the ISS, to get used to doing exactly this. The gravity issue isn't a large one: on a 90 to 120 day mission to Mars, the level of bodily deteriorating isn't that big. We don't have a lot of data for the exact "how bad is it" but I'd strongly suspect that 3 days in microgravity and then 2 years on the Moon is going to be much worse than 90 days in microgravity and then 2 years on Mars.
No, Mars is totally not feasible at the moment, simply because it'd take too long to get there
A 90 or 120 day trip just isn't that big an issue. People have spent far longer on the ISS and managed fine.
Having a moon-base would make it more doable, as it becomes quite a lot easier to build a massive ship to accommodate three couples, so they won't go insane and murder each other, have enough spare parts, and have enough food stuffs to reach Mars and go home again
People don't go insane and murder each other nearly as much as they do in movies. Again, look at submarines. The degree to which there are psychological issues is drastically exaggerated.
What you'd need to get there would need to be massive, and something of that size simply can't be launched from Earth, but it can be constructed a lot cheaper in orbit of the Moon.
One of the lessons from the ISS and Mir is how incredibly difficult and expensive in-orbit construction is. Now, we've learned from it but its still a big issue. If you want to send 12 people then the most pessimistic estimates give you around 250 tons of stuff for a 2 year mission. That's only slightly higher than the Starship design, which is capable of being built on Earth, and masses about 5000 tons. Serious on Earth-designs for rockets have been bigger than that. For example Sea Dragon was going to mass 18,000 tons. And you can also do things to reduce the difficulty by launching multiple rockets, say one with the humans and the stuff they need for the first few months, and then another just full of cargo.