To add to the loaner car idea, experienced racers can also offer to help setup and/or fix a new racer's car. This can be done during a club race or the more experienced racer can take the car home and fix it before the next meet. Often newer/less experienced racers make simple mistakes when building their kits that adversely affect the handling.
I wouldn't consider myself the best setup guy, but I can at least help most newer racers get their car mechanically sound. This week I helped a younger racer with a TT-01 and ended up finding the shock shaft was missing an e-clip (not) holding the piston in place. I quickly fixed their car before their lower main and they earned a bump up to the A-main. There are still more issues on that car, but at least they went home happy.
After I found the problem and showed it to them, I made the point to emphasize that I've made the same mistake in the past. This helps a newer racer feel okay that they made a mistake when a more experienced racer has too. Sometimes it may take a few times for a new racer to learn from their mistakes, but they will have more fun if there are people who are helping them.
I realize that some people feel that newer racers need to learn and do everything on their own if they are going to take this hobby seriously. But on-road can have a steep learning curve. Rather than complain about the new guys driving poorly, take their car out for a test drive and if possible make it easier to drive. While not everyone is a good driver when they start, most will do pretty well if they have a decent car to learn with.