a- If people starts to buy other Bitcoin competitors, it would make the Bitcoin network less secure
The Security of Bitcoin is not related to how many Transactions Binance has. It is related to Mining Bitcoin, not to the number of Transactions.
b- Everybody wants the Bitcoin network to be the most secure, the buyers and the sellers
True for the Buyers maybe, false for Sellers. They probably do not care as soon as they sell.
c- Then if the Bitcoin network becomes less secure, then all parties, buyers and sellers, are forced to accept a higher Bitcoin price to make the network more secure, and this price increase discourages/block people from investing in competitors
No body is forced to accept any thing. A LOT of Money went to 'competitors' years ago and Bitcoin never became less Secure. Like I said above. The Security of Bitcoin is not dependent to sales.