So with Bitcoin Etfs becoming a thing will we have to worry about 51% attacks or anything negative like that?

I may be on a train of delusion but I wonder if this is one of the few MAJOR vulnerabilities of Bitcoin and cryptocurrency as a whole. It doesn't sound like its impossible to accomplish. ETF's overall sound really good in terms of price action for Bitcoin, given how gold's price reacted to its first ETF on NYSE. BUT it sounds bad due to all the Bitcoin being bought up by one entity and potentially assuming control over the network. Maybe there is some fail-safe within the tech that I am unaware of but hopefully this all goes well. What are your thoughts?