VinnieFsee what I wrote above. Yes, it could absolutely work to your advantage in an area with multiple ski areas to choose from.
You say they would loose all sorts of weekend warrior money. Do weekend warriors buy seasons passes or day tickets? Most of the ones I know buy day tickets. If this means they buy a pass instead and split it with a friend then are more inclined to ski that hill solely as a result this is only a benefit. Choice needs to exist.
I define people who are weekend warriors as people who go up regularly. Those people are most definitely buying season passes. I go to Mammoth 3 weekends a month, which is 6-7 days of skiing. My Mammoth pass costs only 700, which is very cheap. You only have to go 5 days for it to pay off. If someone only goes to Mammoth 1 weekend a month it still makes sense, as they would ski about 12 days a year, which is less than 60 dollars a day. Mammoth sells a TON of passes to people in southern California who fit this description, in my guess is that the majority of people who buy season passes to Mammoth use them fewer than 15 days. This would allow people to borrow season passes from friends who are only using them one weekend a month. That costs Mammoth a lot of money, because day tickets are usually 150 to 170. If someone can borrow a pass for a weekend Mammoth is out at least $300 for that person. You could have a situation where eight people buy 2 passes, each weekend a different pair of people goes up to use the two passes. You end up with a situation where Mammoth sells to passes instead of 8, and loses $4200. In a populated area like socal most people are going to know someone who has a pass, so Mammoth would lose a ton of money in lost day tickets among people who go up once a year, i.e. won't buy a season pass. A mountain like Mammoth would absolutely get crushed, in an area like socal, or Denver, where a mountain sells tons of season passes the mountain would get killed by people borrowing a friend's pass instead of buying a day ticket. Denver has a ton of people who buy season passes, Vail/Breck would get killed if people were to borrow passes instead of buying their own. There would be too many people to borrow passes from, they would lose a ton of money on day tickets.
Personally, I have no interest in sharing a pass with someone. I want to be able to use mine whenever I want, so it does not make sense to share. For someone who goes 10 days a year, sharing makes sense. But why would Mammoth want to do that? One year they sold 25,000 passes, which is 17.5 million in revenue before the snow even falls. The majority of those are to weekenders, people who live down in LA. If they can share, people who ski 10 days or fewer will probably only share a pass, which could cost them thousands of passes, and millions in revenue. Also, you would lose revenue because people who have friends with passes would just borrow, instead of buying a day ticket. For a mountain like Vail or Mammoth it simply makes no sense.
I don't think shared passes would cause people to buy more passes. In fact, it would be the opposite. Maybe in an area with several little mom/pop places competing you might be able to make something work, but for a big mountain it does not make sense. I should also add that being able to share a pass would not make any difference to me. I would rather pay $700 for a full pass than 175 for a pass I would share. I think resorts would charge more for a shared pass, which is a lose/lose. I like things the way they are, season passes are pretty cheap in lots of places.