Let's entertain this argument for a moment.
Pretty sure the number is the mid to high hundereds of coins, and not in close to total production.
1) You buy mining gear with fiat that is not needed elsewhere. As this fiat was available there is no need to dump coins in a bear market. Wait for next ATH. Net market pressure: Up.
That would be hobby mining.
Hobby miners can obviously obviously do as they please. They could sell or hodl. The distribution is obviously up for debate. Assuming hobby miners account for a total production of 1000BTC a day and 50% sell that would mean 500BTC entering market a day (fiddle with those number as you want).
Net effect: slight downwards preasure on market.
Even assuming no one sells coins the market pressure is simply neutral (supply and demand on exchanges isnt changed).
2) You take a loan, mine and sell regularly to pay the loan back. You do not sell 100% of them regardless of price because you did your calculations beforehand. The coins you do not sell are now unavailable to the rest of the market, increasing scarcity and therefore price. Net market pressure: Up.
b.) Farms have expenses and can only burn through so much fiat before they have to sell at least some. I expect them to sell mainly off market. E.g. KNC advocates the concept of "clean" coins, that is freshly minted untainted coins, and says those should be worth more. Since there is no way to sell those at a surchage at exchanges they will sell offmarket.
Net effect: Coins sold off market dont directly affect price on market, but reduce demand on exchanges (since buyers did not need to visit them).
3) You are bad at math and mine at a loss. You either turn off your miner or bleed money until you end up in the gutter. Net market pressure: Down, but temporarily.
That would be those "gold rush noobs". Funnily enough there actually seem to be quite a lot of those. Since a lot of miners sell used mining gear on ebay etc., at prices which look like a bargain compared to original price but with no chance ever even getting close to a net ROI. Since thats mostly used equipment the effect on BTC supply is fairly low. Possibly there is a psychological effect though, being basicly scammed (being sold a "gold shovel" that has no reasonable chance of getting the investment back may inspire that feeling) and never considering using BTC again (and possibly even warning others).
Not being a miner myself, it's possible I missed something. But so far, it looks like sustainable mining is good for the price.
Had a 2012 BFL preordered rig myself. Back then, even at ~$10 per coin, it would have been a fantastic investment if it had been delivered in a timely fashion.
I think the main fallacy you make is that you consider freshly mined coins that arent sold on market as upwards pressure. Its simply preasure neutral, since coins dont enter market. It could actually even be considered donward pressure, if fiat was spent to make the purchase, since it could have instead been used to actually buy coins on market.
I'm actually looking to be proven wrong here. But with logic and numbers, not trolling. Thanks in advance.
NP. Basicly i agree with that "miners selling thousands of coins" (at least on exhanges) is probably bullshit. On the other hand i dont know if that is actually good news, since it raises the question of what happens if miners actually have to sell thousands of coins. Assuming e.g. that in case 2) a farm will only sell enough of market to cover running costs the amount sold will naturaly increase as price goes down, while at the same time expenses to gain the coins go up (hashing rates increases, either invest more in equipment have a reduced share).