Should semiautomatic weapons be banned?

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I wouldn't want them in my country, but it's a stupid goal for America.

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These questions are always interesting, because there are two factors at play. One is whether such a ban would work (i.e. would have a measurable effect on the level of mass shootings) and th other is more philosophical (i.e. irregardless of any measurable impact, such a ban would be an immoral move that compromises the rights of the innocent). It's similar with say, the argument against the NSA's surveillence policy: some might say the policy is bad because it doesn't work and some say that even if it did stop terrorist attacks, it represents a fundamental breach of human rights irrgeardless. It's a much more interesting problem to measure one's view on the deontolgy vs consequentialism debate than silly trolly problems.

So let's ask questions:

1) Opponents of a ban: let's imagine some social scientist has managed to prove without a shadow of a doubt that such a ban would cause positive outcomes. Does this matter? (this isn't intended as a shaming "gotcha" question btw - even if I was handed evidence that a hardcore policy to intern immigrants without trial would slash violent crime rates by half, it would be irrellvant to me because I believe that this would compromise invaluable human rights)

2) Supporters of a ban: if you were handed evidence that proves, again beyond doubt, that such  a ban would cause only a marginal decline in violent crime/gun deaths/mass shootings; would you still support the ban? Do you operate under a policy that even one more life saved is worth it? Perhaps you don't care either way, and view it as fundamentally immoral that people even posess guns of such a nature to begin with?