Sorry, I'm tired and a little burned out, and I'm responding more waspishly than I should.
Tieflings aren't hellspawn - that's a racial slur. They are born on the material plane (generally), and are 'spawned' by mortal parents; elves, humans, dwarves, halflings etc., not by any hell-born creature. They *might* have a fiendish ancestor somewhere back along the line; *probably*, even. They don't necessarily have one... This is because they are plane-touched, and not fiends. Plane-touching can come about in a variety of ways, and direct siring and interbreeding is only one of them. If you don't know (and you won't in most cases), then by all means be cautious, but don't make assumptions. Almost no tiefling alive today decided to become one. Most were born that way with no say in the matter. It has no bearing on their individual personality or propensities towards good and evil, save in the way they are often treated (without just cause, usually) by ignorant or racist people. Characterising a tiefling as hellspawn is just a derogatory, and not something anyone who considers themselves a good person should engage in.
Yes, they are supposed to be less common; current world events explain the reason they aren't, right now. IT is true ,and an interesting aspect, theat they are often thought about as a race of peopl , but they aren't, truly.... they're just people who, by virtue of their existence don't have any kind of unified culture or history. A tiefling born to elven parents and raised by them would have elven values and customs, and halfling-born tiefling would have halfling culture and custom. Tieflings abandoned or raised from orphanhood often have no cultural background or norms at all, save those they developed in whatever city they grew up in. These would be interesting conversations and character-building explorations to go through - these are the kinds of things that should show up in racial dialogue tags. Not one-off racially-motivated remarks or insults.
The 'no matter how small' is the objectionable part; an imp is just an imp. I'd be far more concerned about someone I saw traveling the darkened streets of baldur's gate with a pacted red cap in tow ready to break some kneecaps, than I would a mage with an imp carrying their books. An imp is not the worst of the worst, and using one is not equivalent to wearing a sign saying that you're friends with terrorists. Someone commanding higher-order fiends would definitely be worthy of concern. Imps, not so much.
Druids must certainly defend the balance, in their personal view of it, and follow a version of whatever natural philosophy their particular circle holds. They are not "'everything must be natural' hippies."; that's ridiculous.
Bruh, if you met an aasimar would you automatically fall all over yourself to befriend them and treat them like an awesome person and presume the very best of them right off the bat without any evidence of the sort of person they are? Somehow I doubt you would; so why give the inverse of that to tieflings? If you would, then how would you feel about it when that aasimar shows you this really cool spot off the beaten track where they can break your legs and steal all of your stuff for being so gullible?
I'm not going to engage with this topic any more; I'm sorry for being aggressive. It's taking up too much of my time and energy, and I'm already being encouraged by people I trust to not engage with the forum discussions as much.
On Topic:
The reason people react badly to you summoning is becuase it's treated in the game design as an aggressive or hostile action, and people don't like you doing it near them. Non-standard summons also cause comments, but the attitude strikes come from summoning too close to a person's general proximity, or from a character seeing you do so to someone else. At least, that has been my experience of it so far. You get the same attitude strikes from throwing a damaging AoE spell close to an NPC, but not hitting them with it, I believe.
