So are we now defending the DM who did this to you or pointing out how the adjudication of the situation was in some way unfair? You seemed to have a negative reaction to it happening. What's going on here?
What is going on is that there is a large difference between applying, in good faith, the right rules to manage familiars, and deciding that familiars have to be killed on sight and not even bothering with niceties, and in particular not about explanations, usually because they are simply none, it's just that the DM dislikes familiars and will kill them because...
That perception is just wrong, where I'm concerned. Enemies will exploit mistakes in some cases. Leave your familiar exposed in combat and they're a valid target. Send them into a dangerous area to scout, expect that they may get killed. Make decisions and prepare accordingly. That's just playing the game.
Again, it depends on the DM and his views. Why would you send a familiar to scout only in areas that are not dangerous ? But you need to be able to assess the risks. If the risk assessment is that it's not that great a risk (an owl with superior perception and stealth, at night, into simple woods), then the assumption is that it will not be killed outright just because the DM has decided that familiars are on the "kill on sight" list.
I try not to assume what players have their characters do.
And yet, the rules assume that characters are heroes, not stupid, and always on the lookout. Assuming that they need to describe every single detail all the time and in particular "I'm watching for danger" is not only unfair, but it slows down the game and it's just waiting for a "gotcha" moment. So yes, by default, I will not assume the worst of the PCs, I will assume that they ask their familiar to be properly positioned. Moreover, the game default is not to use a map or a grid, so if a player tells me that his familiar flies away and gets out of sight after helping his master, I will by default assume that he does so in a manner that actually provides them cover. I will not assume that it stays in the open in a position where it might be killed just because the player did not specify exactly where.
It's on them to be reasonably specific about their positioning. (A map and minis helps with this.) What weapons a monster may have at their disposal will also be telegraphed when I describe the environment. That's part of setting the scene in my view.
On that we agree, but then there are many things which might not be visible and in particular magic, which is after all fairly common.
Anything can be made to make sense in the context of a game based on make-believe. Putting the PCs' resources in jeopardy isn't necessarily about hate.
But putting familiars on a "kill on sight" list smacks of it, that's all, and that's what some of us noticed. It might not be the case for you, but the extreme wording should, in all fairness, be avoided.
It's just part of the difficulty of the challenge that must be overcome and a means to introduce tension.
I hope that you do realise that the game does not need anything like this. It does not have to be a challenge for the players, it might just be about telling a story collectively, using some rules for resolution. On the other hand, some DMs feel that they need a tough world so that players are challenged, it's fine, but it's not the absolute rule, and all manners of playing the game are good as long as everyone is having fun.