I've seen that a few times there lately and it's an unfortunate byproduct of a new sport.
On one hand it's great that there are some new players getting into the sport and enjoying the game, but with that comes the trials of learning the etiquette and respecting the game and other players as well. Of course this is not acceptable, neither is the littering and using Sharpies on the baskets for Aces (write it on your disk!). Hopefully they will run into a similar situation in the near future and realize what jerks they were by not splitting into 2 separate groups and not letting you play through.
However when I play solo, other players offer me to play through and I usually shock them and counter offer to join them. I have met a few local players this way and have also helped each other's game by comparing my skill level with theirs, but have never made a group larger than four. Sometimes this will often lead to conversation about etiquette and rules of the game to new players and introduce them to other courses in the area. So far, this approach has been positive in every situation to act for the "greater good" of the sport.
Good news about the basket. I hope they move or replace it soon.