You have a point about the play faster theme. It permanently drove me away from Isotropic the very first time I played. Goko/MF was not nearly so bad, and frankly, I haven't had a problem on ShuffleIt, but I can believe that some people may experience it.
That does not in any way excuse slow-rolling. If the problem is people complaining about your play speed there are a couple of things you can do:
1. Practice against Bots. This certainly helps with learning the interface, but is limited for non-subscribers getting games against subscribers. Really the only solution there is to pony up and get all the cards. I know that bots are not great to play against, but if you are motivated by learning the cards, bot games are a stress-free way to do that.
2. Explain in chat that you are not slow-rolling, but need extra time to think/read cards/ etc. Hopefully your opponent will be understanding, but if they continue to be a jerk about it, that's on them, not you.
3. Make interim moves. Often when I get to my buy phase but don't know what I want, I'll play my treasures then think, especially on turn 1. That was I show that I'm present and playing, not just sitting there.
4. Once blacklisting is activated, you can always blacklist players who are too pushy about speed play.
Ultimately, I believe that you have the right to play at a pace that is comfortable to you. Sometimes there will be situations that demand extra time to think/read cards, other times you will be able to play fast since there are no decisions needed. I believe that most players will respect this if you are clearly not slow-rolling, and the ones who don't aren't your fault.