There is so much wrong here.
It is pretty obvious that going to the parks is one of the safest things you can do. It has large outside areas, masks required, all things that are known to prevent the spread. It is safer than going to the store, eating out, any office job, and many other activities. Having these options open provide a much needed boost to peoples mental health which cannot be understated. There is also the responsibility of people to know who they are hanging out with and what they have been doing. We know the main culprit of the spread is indoor areas with people close together and no masks (bars/nightclubs).
A large number of HHN workers specifically sign up to work that event so if they do they must feel comfortable enough to work.
It is not a once in a lifetime event, it literally happens every year. I figured it being HHN 30 would have given that away. Every year people can't make it to the event because of some reason and those people move on and have a solid life so missing out on the event for one year (will happen either way for those people) is not a big deal. The last part is the biggest falsehood and probably the most harmful. Being "responsible" will not end this sooner. Yes it will lower infection rate, but it will not make it go away. So many places that have "done a good job" following the rules have had to shut things back down after opening back up. It will by you time but the virus will still make its way around until there is a cure.
Going to the parks is NOT one of the safest things you can do. The briefest of consideration reveals how absurd this take is. If you go to the park for one hour, keep your distance from all other humans, don't go into any restaurants, stores, or rides, and then leave, its fairly safe. Noone does this. You go to the park for hours - do you go to the store or eat out for hours? There are thousands of people with you at the park - are there thousands at the store or restaurant? Every interaction is a possible vector, and the number of interactions you have at Universal vastly outnumbers those at the store or restaurant. Oh, and there are examples in this thread of the fact that compliance with mask and social distancing guidelines is not particularly good. And remember, folks can have their masks off to eat or drink as they walk around. We know people have gotten sick at Universal. The Orange County health department has confirmed this even as they spun desperately to downplay it - plus we have reliable TM reports. So... no Universal and WDW are not remotely safe.
Its also really, really funny that you rightfully point out the dangers of indoor areas with large numbers of people. Because Mummy, Gringotts, Bourne, ET, Fallon, Cat in the Hat, Shrek, Despicable Me, F&F, MiB, Spidey, Poseiden - none of those are integral to a trip to Universal. And surely, SURELY, when the lights are off and people are preoccupied with enjoying themselves and the rule is literally unenforcable, every single mask in those havens of recirculated air stays on at all times.
HHN events are unique. They are not repeated. And their is an ENORMOUS difference between missing the event because you can't get off work and missing it because you are behaving responsibly during an uncontrolled international pandemic that has cost the lives of hundreds of thousands of people. One is an event unique to the life of the individual, one is a massive shared catastrophe that some people are too scared and/or selfish to acknowledge.
And to address the biggest piece of nonsense in your response - with responsible behavior this virus CAN be controlled to the point that recreational activities can be resumed with relative safety. Look at a few minor examples like most of mainland Europe, Taiwan, New Zealand, South Korea, etc., etc. Pretending those examples, involving millions and millions of people, don't exist is deeply dishonest. Being responsible can end the raging epidemic we are seeing right now in America. Had we been responsible months ago, talking about holding HHN would be a reasonable conversation. But we weren't, largely because people peddled self-interested, bad faith lies like "being 'responsible' will not end this sooner," which is really just a way of saying, "I wanna do things like normal and I'm pretty sure I, personally, won't suffer too much, so who cares about the pandemic."
You know what will will help mental health? Not having thousands upon thousands getting sick and suffering every day and being able to return to normal activities without risking your life and the lives of those around you.