I havn't seen any attacks. What I see the most is those that are time traveling that want to justify themselves.
Anyone can play the game like he or she wants true. So if people don't want to have to do anything with time travelers in the game, they are free to set those parameters. The knife cuts two ways.
You can say you want to play like you want to, someone else can say he doesn't want to play with you under those rules.
For me there is no discussion I do not mind time travelers, at the same time I do think they might somehow break down the fun of the game. (For those that are tempted to sell nook mile tickets for 400.000 thousand bells. They kind of wring out the fun of exploring the island themselves, and getting easy bells... Which makes the game more boring in my opinion. Of course there's people happy with it but I rather not for myself, so I don't advice others to do it.)
If time travelers are angry that they are being excluded by someone, I will tell them that they also exclude others. I for example cannot compete with the economy cause of time traveling. Do I mind? Not by much as this is the type of game that attracts all kinds of crowds, and that means there's also grown up people that like to share and play together.
Giving and receiving gifts is way more fun then the whole trading thing. I like to play the game with others as if I'm a villager, share, ask favors, help people etc... I think it's fun.
I made a friend the other day in Animal crossing and she said she would keep an eye out if she saw any outfits I would like for my character. I mailed her a piece of furniture I found of which I thought she would like it.
This is how I like to play and as long as there's people that agree with my way of playing I'll have friends enough.
Those that like to timetravel and become rich in bells and all that jazz... I'm to old for that now, for me animal crossing feels nice, I like the patience it requires.