I've had mixed experiences. On some days, I've been approached to form alliances by basically everyone. Sometimes that's worked out fine. Sometimes it hasn't.
In the past, if I saw a ship approaching I'd tend to assume they were hostile but there was a chance they might be friendly. Now it's the opposite. It makes judging intentions both more difficult and more critical. If you take a chance and let a ship approach, and they turn out to be hostile, you've lost your tactical advantage and it may be too late. Some ships fly alliance flags for that very purpose. They use the flags to get close and then spring a sneak attack.
Some crews join an alliance to take advantage of a situation. Recently my brigantine crew joined a battle against the skeleton ships. At one point we had three brigantines and two sloops in the fight. When the battle was won, one brig crew stole most of the loot and sailed off for the opposite end of the world, while everyone else sailed to closer outposts. They used the confusion of so many ships to their advantage. When they were away, they broke the alliance before they started selling, presumably so we couldn't find them. Of course that meant nobody else got their fair share of the loot, which was definitely a dirtbag move. By the time everyone realized what had happened, it was too late. We got some of the loot, but the rogue crew got the lion's share and shared nothing. The alliance fell apart after that.
The other day we had an alliance with two brigantines and a sloop, and rolled up on an active skull fort with another brigantine already there. Soon after we arrived, the fort fell. We asked the brig to join our alliance, and they complied. Really, what else could they do? I'm sure they felt they had little choice at that point. They still got all their loot (we let them load it on their ship) and we each got a cut. Not long after we all went our separate ways, that same brigantine began attacking all the allies, one at a time. We battled them for a while until we got sunk, then went on to continue our voyages. I'm not sure what transpired after that.
Clearly, alliances have changed some of the dynamics of the game. Have they killed PvP? Absolutely not. I do think it's fair to say more crews are teaming up with other crews than ever before. But a lot of those crews were not PvP oriented before alliances. Alliances have simply given them a major tool for cooperating with other crews, and that's not a bad thing. I think most people who were PvP oriented before alliances are still PvP oriented. In some ways, they may find it easier to approach potential victims. Whether that's a good thing or a bad thing depends on which side you're on.
I think over time this will all balance out. People will likely learn to be more selective in those they ally with. I agree that there's no real downside to not joining an alliance, and maybe that's a problem. But alliances are still fairly new, and it's hard to know for certain how the game will evolve. So...we'll see.
For myself, I still play basically the same as I did before. I tend to be suspicious of other ships on the horizon, especially if I'm soloing in a sloop. I usually avoid other ships, unless I've already dumped my cargo and feel like taking a chance. I don't let anybody board my vessel unless they've earned my trust. When any ship approaches, I keep my guard up. Even if they're allies.
Last night I docked my sloop at Golden Sands and sold all my loot, just as a sloop and a galleon approached. It wasn't clear what was happening, but it piqued my interest so I decided to stay put and see. I noticed the sloop was flying the Jolly Roger, while the galleon flew the "offer alliance" pennant. Both ships pulled into the outpost. Someone was spamming out, "WE'RE FRIENDLY!" "LET'S FORM AN ALLIANCE!" Hmm. Then as the sloop was passing, they fired a cannon over my ship. Pretty sure it was a cannonball and not a player that went flying over my sloop. It was just one shot, so I didn't return fire immediately. Instead I pulled out from where I was docked and positioned myself advantageously to the rear of the sloop, ready to blast them. I decided to join the galleon's alliance at that point, since the sloop seemed to be the "rogue" ship in the situation. That would later prove to be a huge error in judgment.
One of the pirates I'd seen on the deck of the sloop started to swim over to my sloop. I warned him twice, "DO NOT TRY TO BOARD!" When he came up the ladder I killed him, as promised. By then I'd had it with the whole situation. I unleashed my cannons on the sloop and sank them. Immediately after, the galleon (my "ally") started firing at me. Hmm.
I tried to talk to them, but to no avail. I killed a couple more boarders, but my sloop was sunk. I clambered to shore, still trying to parley with the nitwits. I could hear the sounds of battle on board the galleon, and it slowly dawned on me that I'd picked the wrong side. The boarders on my sloop had all been from the galleon all along. Then someone tried to snipe me, and that was it. I'm not great at PvP, but I'd had enough of that nonsense. I boarded their galleon and killed them. All of them. I rammed their ship into the outpost.
Of course it was a hopeless battle, since they kept spawning back on the ship, and eventually they killed me. Once back on my sloop, I disbanded the alliance and called it a night.
