There is so much misunderstanding here...
A scientific theory is not indisputable. Ideas and hypotheses do not "graduate" into being theories/facts. Some theories can be proven, but most can not. Just because one unprovable theory (gravity) is pretty much undisputed, doesn't mean that all theories are.
The theory of evolution is disputed because the evidence is not nearly conclusive (far less conclusive than the evidence for gravity for instance). Evolution as a mechanism for global search has been proven in the abstract, but that doesn't necessarily mean that it was also the mechanism by which life has changed throughout the ages. It means that it could be. There are of course many clues that are consistent with this view (some people like to call this evidence).
To be honest I think the primary reason that so many people believe in evolution is that there is no real scientific, alternative explanation. That doesn't mean that all criticism is invalid though. For instance, even evolutionists admit there is a "missing link". But a far more significant criticism in my opinion is that people are disputing that the preconditions for evolution are met by the building blocks of life. The argument is basically that the fraction of configurations of amino acids that are viable for life is so small that it would take many times the lifetime of the universe to get one by random mutations. It follows from this that only decreases in complexity and variety are plausible, so we couldn't have evolved from single cell organisms. At most we could have (d)evolved from slightly more complex proto-humans (and dogs from proto-dogs, etc.), which is nicely consistent with the intelligent design view.
I personally still believe that the evolution theory is probably true, but I haven't been able to come up with a convincing counter-argument for this yet. If anyone does, I'd be interested in hearing it. But if you can't, maybe you shouldn't be claiming that the theory of evolution is indisputable, and you should instead keep an open mind like the OP suggests.
On the other hand, as some people pointed out, this is the internet. And on a forum like this, with high school kids and anonymity, you are bound to get discussions that are less than scientific. I was a lot more surprised to see that this phenomenon also occurs with real scientists who are posting under their real names in LinkedIn groups.