Joining NATO may actually place Finland and Sweden in greater danger than if they stayed out. You could be volunteering as a target of Russian ire when you are not already. As barbaric as Russia's Ukrainian invasion is, I do not think it is evidence of Russian expansionism. The Russians told us that bringing Ukraine into the western orbit was their red line, that they considered it an existential threat to their country, and that they would fight tooth and nail to prevent it from happening. They were emphatic about this. Would that we had listened to their warning.
They are having a hard time taking Ukraine, and if they wanted to go any further westward that is into NATO territory, where they absolutely could not make any realistic progress with conventional means, and NATO has a powerful nuclear deterrent. Russia's current interests are likely in those same countries where it has had a more recent historic influence, whereas Finland and Sweden have long been within the western sphere of influence. Although the Soviet Union had designs upon Finland and invaded 80 years ago, it did not managed to acquire it.
Let us suppose for a moment that Russia has no plans to take Finland and Sweden by force (and have they given any indication that they intend to do so?). Given the Russians know what their own plans are, and we assume for the sake of argument that they are not to interfere with Finland and Sweden, how will a move to join NATO by those countries be received by Russia? Remember, NATO is an implicitly anti-Russian military alliance. It seems more an affront to Russia, rather than a necessary defensive measure, and will likely feed the Russian perception that NATO is plotting to encircle them (not wholly unjustified, particularly if NATO formally extends an invitation to Finland and Sweden).
NATO's actions are, by the articles of its charter, supposed to be undertaken to promote stability in Europe. That instruction is rather open to interpretation, and actions contravening it can be justified by the simple act of self-deception, but given that there are doubts as to whether admitting Finland and Sweden would promote stability, I think it is better to maintain the status quo than to admit them. Instead, Finland and Sweden should wait until there is an EU defensive pact.
A military incursion into Finland and Sweden would require a lengthy build-up of an invasion force. The Russian armed forces are likely to be almost spent, even if they are successful in Ukraine, having experienced heavy losses of men and equipment. It is unlikely that they will have a further appetite for more invasions in the foreseeable future. Finland and Sweden were happy to remain outside of NATO during the last period of clear Russian expansionism in the Soviet era. The desire for their peoples to join now, then, seems more about trying to teach Russia a lesson for its Ukraine invasion, than a necessary step to protect themselves. It seems that the two countries have been caught up with the groundswell of popular western sentiment for punishing Russia over its Ukraine invasion.