The existence of a secondary market helps the business to sell their IPO in the first place. Additionally they can raise more funds by selling additional shares.
Additionally the people who own shares own the company so what benefits the shareholders benefits the company and vice versa as their interests are the same.
> If you buy stock from other stock owners it doesn't help the business
Incorrect. That's what keeps the market for the stock liquid, and that contributes to value which the company can exploit through future stock issuing. Not to mention the indirect benefits to stakeholders within the company in terms of price and liquidity.
No, because your holding increases the price until someone else decides it's time to tell. In other words, the lack of liquidity increases price. Regarding your original question, that increase is GOOD for the company because it can raise more money for selling the same amount of stock.
Additionally the people who own shares own the company so what benefits the shareholders benefits the company and vice versa as their interests are the same.