What other proves do we need when just by barely observing the market it's very obvious some manipulation are ongoing. Talk about inside trading, if altcoins get traded by insiders with valuable information on some positive development on the project like new exchange listing, major news etc talk more of bitcoin that can be easily dumped or pumped by the whales which obviously exchanges are part of. Tether can be printed from thin air and used to buy the bottom occasionally probably pushing the price upwards. Exchanges like bitfinex is guilty of this.

I strongly believe exchanges are playing a negative role in the space, mainly because of price manipulation. And if -like in any society- evil doers are not going to pay a heavy price, we all stand a lesser chance to succeed in our investment. There should not be a possibility for someone to short or long a crypto, sell or buy, unless he really holds it!
I watched this debate between Peter Schiff (Gold bug) and Anthony Pompliano (Bitcoin bug), a rare piece of what you call a high quality debate that you could barely watch these days: https://www.youtube.com/watch?v=Wigz8z6Vm3U

In this debate, Peter Schiff said yes his company lists Bitcoin as a payment option but they don't accept it themselves, they have instead a payment provider called Bybit that pays them in dollars. Which makes Bitcoin of course more expensive to pay with since you now have a middle man.

And I think he's right in not accepting Bitcoin. Exchanges would pump the hell out of Bitcoin, dump all the bitcoins they could possibly have to buy gold and then let the market return to its normal place again.... This of course plays against Bitcoin mass adoption.

I think the OP is seeing it differently. Exchanges are promoting crypto adoption as you said they open doors to newbies and of course to old timers as well. The more exchanges we have, the wider options that the community can go to. But only few of them are to be trusted as a lot of them will screw the users' funds.

Well the altcoin explanation was used to stressed my point. The fact is the exchanges can manipulate the market by creating either bullish or bearish scenarios although that's not a regular occurrence. Few days back, OKEx exchange suspended crypto withdrawal as one of the key holders was missing which was later discovered that Star Xu got taken by the police. Bitcoin saw a flash panic sell that dipped the price from $11.5k to $11.2k although some recovery has occured.

Exchanges can easily cause panic in the market and this isn't the first such scenario has be observed. Few years back, Bitcoin suffers wild weekend after yet another Tether scandal. There are many more events like this that the market has experience some downtrend as a result of a particular exchange.

The bitcoin market though is getting nature as not all exchange related event have an impact on the market that easily but their influence can still be felt.

Btw the problem is that exchanges really try bad things. For example, binance bought coinmarketcap, the major cryptocurrency price checker. So, I think it's unfair agreement and is not good for cryptocurrencies.