I wouldn't even say it rises to the level of "expressing skepticism"
per se. It's just literal
ad hominem. Ad hominem is a logical fallacy precisely because a good argument is a good argument regardless of who is presenting it, and likewise a bad argument is bad on its own merits.
There is more that could be said here, but, really, if you take this as your default approach to analysing things you read on the internet, you'll be headed in a good direction the vast majority of the time. It's not a completely black and white thing; for instance one certainly should hold out a healthy level of skepticism if, say, the message and the speaker seem to be completely incongruous, but mostly, let ideas stand on their own.