Because unfortunately, sometimes violence isn't the answer, and can make things worse. There's other answers.

Gosh, I missed these. They were always pretty cute.

While purging everything is good and all, sometimes you just need to work things out. So you can get allies to purge with later.

Why? "Because being nice is it's own reward!" and sometimes comes with extra perks ^^

because if you don't you will have to fight sans

you only fight sans if you go out of your way to kill everyone

if you just murder whoever you encounter, that still gives you a neutral ending

Holy crap, you just made me realise.

Frisk is a goat lady, Asriel is female, Toriel is a mute chubster, Asgore is a MILF, and the dummy is a Mew Mew.

What is Sans like in this timeline?

Let me give you an example, if a small child steals part of your lunch do you beat them to a pulp or do you confront them in a less violent way?
If a big buff guy is bugging you by flexing nearby do you murder him or do you walk away or maybe think of something else?

acting is how you get the big tips, no xp though

Because a battle avoided can be considered a win too.
Heck, it's clear there's more than just these two down here, you're gonna need allies.
The more people you have on your side than against, the better.

Because if you kill monsters, you'll piss off a certain hyperactive fish-lady you haven't met yet who will then want to kill you.

And because you're a monster yourself now, or... well, part-monster since you still seem to have a human soul with a determination aspect, your body isn't quite as, well... let's just say "solid" for lack of a better word, as it normally would be. Monster physiology is extremely vulnerable to attacks with killing intent.

Oh, also, sparing monsters gives you gold you can spend on items.

friends are better then foes. fight bad, act good.

So, that's a game, there are a few different endings, if you want to get the best ending, you shouldn't hurt anyone here

Because the feeling of not punching things at random fills you with…self-control?

These are real people you're in a universe that just so happens to line up with a game it doesn't mean that it is one

Because deep down you are a good person and wouldn't deck someone in the shnoz ?

OOOoooor maybe because you are a goat-lady(?) and getting into fisticuffs whilst wearing heels has got to be very tricky and its all around safer for you to not.

Cause Acting is fun. Even if its weird. :3

because if you ACT you can turn into a FLIRTing machine, use the FLIRT Frisk, use the FLIRT

just play along for now it's not like she'll be following you everywhere

Definitely a stranger in a strange land situation. Might be better not to fight them cause potential they can help you out or maybe give you some idea where you’re at.

"It's a lot less exhausting"

Use Act to do armpit farts, don't do actual farts or you might poop.