Even were the Universe to be finite, what makes you think we have actually found the outer bounds, and that we are even capable of knowing it’s mass?
Seriously? If the Univervse was considered ifinite, then why would anyone screw around with the multiverse concept? The concept of infinity is a purely mathematical construct, of which there is no evidence that it is anything but an effective mathematical tool.
So the let take a try at your rhetoric, "the concept of the Infinity (another theory) is fairly presumptuous.
If we continue down that path then who is to say that we can really know anything, since everything we know or understand is based on unknowable or unprovable theories?
Not everything is based on unknowable or unprovable theories.
There are many things we accept in theory, that we may never 'know' because we will never be able to prove them scientifically. It is not necessary that we 'know' in order for things to be, or to work.
Take magnetism or gravity, for example.
(someone already answered this) Because the theory the Universe is finite does not fit with the scientific evidence and mathematical calculations. (i.e. why they had to make up Dark Matter). Therefore, they came up with the multiverse theory to explain the inconsistencies.
The concept of infinity is a purely mathematical construct, of which there is no evidence that it is anything but an effective mathematical tool.
As are the roots of negative numbers, yet they are used in science.