Wait a second, you think Sweden consider joining NATO not because it feels threatened by Russia?
Why then?
Baltic states, Kaliningrad, Gotland. Connect the dots.
IF for whatever reason Russia and NATO drifts into conflict over something involving Narva, Latvia, Kaliningrad etc., whether involving the Baltics, the Poles, both or some oher constellation, the strategic situation in the Baltic says odds are VERY low on Sweden being left out. Mostly because whomever controls Gotland decides whether the Baltic states or the Kaliningrad exclave are at all defensible.
Swedish fears, as they are, occur over the situation in the Baltic states, and go back to the dangerous Russian policy declaration of giving itself a unilateral "right" to intercede on other countries based on how the Russian political leadership interprets the situation, including who is Russia enough here.
As long as that was simply a policy statement, worrying as that might be, it was mostly shrugged off and Russia and the EU continued business as usual.
But then we have had first Crimea and then eastern Ukraine.
This is about collective security, and the reduction of uncertanity. At some point removing some of the uncertanity about what stance Russia might or might not take by joining NATO becomes reasonable. Not least since NATO comes with security guarantees that Sweden currently lacks altogether. The Cold War was a funny period in that sense, since Sweden wasn't part of NATO but HAD outright security guarantees from the US in the case of a Soviet attack. Currently it has literally nothing in the event Russia gets embroiled in something in Sweden's vicinity — which is what the real risk is assumed to be — not Russia attacking Sweden, but Russia sliding into conflict elsewhere, and Sweden becoming embroiled. Gotland provides the most dangerous scenarios.
And anyway, on sea and in the air over the Baltic, and now through diplomatic/political channels as well, Russia is already displaying behaviour and making pronouncements in Sweden's — among other's — direction that, whatever the hell it's supposed to mean, at the very least does not qualify as friendly.