Sweden has history of neutrality and partly it's in their identity. That is why NATO membership is significantly more difficult for Swedish. It's evident in their media, and leading Social Democratic party is somewhat split there.
It might be that Sweden sends the NATO application without vote in the parliament with just vote in defense committee. Which means that Sweden might end up sending application earlier since in Finland the process must go through parliament.
The "neutrality" was originally forced on us at the end of WW2. Maintaining it worked ok for co-existing peacefully with our eastern neighbor. In reality it ended in 1995 when we joined the EU. Back then there was talk that the EU is going to have some sort of co-operative defense, but that hasn't materialized into anything concrete, because NATO is in reality already providing that function in Europe for most of current EU members.
I suppose the main argument against us joining NATO is the perceived risk of getting pulled into some local conflict of dubious nature far away from us.
Edit: Personally I would prefer an European defensive alliance without US involvement, but such an option is not available at short notice, so I'm willing to accept NATO for the time being.
Edit2: I should point out, that me, and IMHO the current generation of Finns in general, don't have anything in particular against the Russians, as long as they manage to keep their tanks and missiles within their own internationally acknowledged borders. We just don't want to become them.
At least for a younger generation, that isn't a big deal at all. Finnish neutrality was realpolitik after WW2 and pretty much everyone understands that Russia/Soviet Union is/was our only realistic enemy in case of war. Neutrality is bigger thing in Sweden as they managed to skip both WWs.
If you ask Putin being part of EU is very much not being neutral no matter what Finland says and under the Finno-Soviet treaty we were quite clearly under Soviet influence and neutral only in some legal fiction.
1. The invader would suffer a massive penalty for their reputation: didn't stop them from invading Ukraine.
2. The invader would be hit with massive economic sanctions: see 1.
3. Even unassisted, we would be able to mount a defense that can cause major losses to the invading force: see 1.
4. Even though there's no formal defense pact, surely the west would come to our aid: Putin says "serious consequences, remember we got nukes", west backs down.
And as a bonus:
5. If, against all odds, they decide they still want to invade and we get no help from the west, there's no point to actually fight back because they'll crush us like a fly in the end, so we should just surrender immediately: looking at Ukraine, this is no longer obvious.
Usual caveats apply, but I believe the main benefit for NATO is to prevent point 5 from happening.