I think some people have a real problem understanding the concept of free speech - complaining that other people are allowed to express their opinions too? Oh gosh, the outrage, the humanity, when will such persecution end ...
If you don't think people should be allowed to express their opinion of Muslims and Islam then you are against free speech. Period.
Why exactly should you enjoy free speech and others not? Why should one person's narrative be allowed to override other people's - especially when, in this case, it is clearly based on utter ignorance of the matter at hand. Having an opinion is great but basing it on some actual knowledge and research is better.
What settles any disagreement are the facts and the arguments put forth. If you have facts and logic on your side then it doesn't matter how unpalatable some find the conclusions, the truth doesn't give a rats ass about your feelings.
When it comes to "what is Islam" I don't think "I know a nice Muslim" is anything more than a complete non-argument. It's like trying to debate what the WTS does and what JWs believe based on the JW lady who brings cakes to work. I'm sure she's lovely and they taste great but it's irrelevant to the discussion and is nothing more than a weak trick - especially when it's used to try and shut people up. A counter argument devoid of actual content and argument.
If anything, it is more of a "no true scotsman" argument - you're really dividing up Muslims into nice ones and non-nice ones then declaring everyone in the nice group as real Muslims and everyone in the non-nice group as false.
Except that is reverse logic at it's finest ... we don't define Islam by what we like, we define Islam by what it is, and it is an evil ideology which causes many of it's followers to hold loathsome opinions and to do unspeakable acts. "No true Muslim would kill jews" simply isn't true because the definitive perfect example of a Muslim was Mohammed and he killed hundreds. Same argument for treatment of women, raping children and lots of other things. There is a reason lots of vile things are not just excused but openly practiced in Islam controlled areas - because they are what Islam is.
Does this mean that there can't be "nice Muslims". Of course not, there were nice Nazis who did great things during the war. But it would be disingenuous to suggest that they were as good a representative of the Nazi ideology as any others were.
The difference with the attacker in Portland is that there is no basis in his religion for him to attack people. It's actually counter to the teaching of most Christian sects. That's why no one has any trouble condemning him. Imagine though that the bible said to behead non-believers and kill them wherever you find them. First, I would question why anyone would want to be identified with such a hateful religion and second ... wouldn't he be a better adherent of it than someone who did not follow the commandments that dictated what it was to be a true believer?
Where people get mixed up is being able to say "someone is a better Muslim because they are a better adherent of Islam" were "better" in this case also means "much worse human being".