Some of them will, many of them won't.

Many gamers set themselves a budget how much they spend on games per month/year. They won't spend more money if they can't buy or sell games on the used market anymore... they would just buy less games or wait for price reductions to stay in that budget.

Well there is no Gamestop where I live. There's GAME (some say it's just as bad) but I've found a decent little second hand place in my town which will also do pre-orders. The the publishers piss me off, I get the game second hand from them. If not, I do a new order through them.

Depends on what the microtransactions are for. If it's just some skins I'm fine with it. If it's more akin to Battlefront 2's lootboxes I'd go with the used option, even if I much prefer buying things new.

I bought used games and new.
I bought new games if I want to support the devs so I do this mostly for Japanese games. I bought Uncharted all new aswell. I also buy new games if the CE is good. Watch Dogs 1.

I bought used games mostly for western games and some Japanese games normally from big publishers like Capcom or SE. I also buy it from other users as well.  We don't have gamestop here and mostly Gaming stores here sell new games. It will be rare for you to see a used games from official seller here.

Although at the moment it's rare for me to buy a used games. Normally I wait for Flash sales and other sales on PSN.
So I was able to buy a lot of western games that way.

PSplus games also helps a lot.

Gamestop already paid devs for that used copy. So unless you resell it back to gamestop it is basically no difference with buying it new, because you are still removing one of the copies from the store that someone else could want to buy, therefore Gamestop would have to order more copies.

I prefer the plug and play era (Atari-PS2) the most so I will go used games.

That's a very important point that I forgot to address. I guess either way, you're still helping out the publisher.

Easy... New game and don't spend any money on MT. The message to publisher is this "people want your games but they aren't dumb enough to buy your stupid MT“

On the BF issue, I don't have the game yet (big backlog and not much time to play games is the reason for that) but I plan to buy it because I'm not bothered for the 2 or 3 guys in a 40 player map to have better guns than me (because they went the easy way and bought MTs), the same way I wasn't when a unemployed guy had better guns than me because he just have more time than me.

Tell me if it's any fun. I might end up picking it up used from a smaller store later on.

Yes, I would like to give money to the actual producer of the game, thank you.