The Sweden Democrats are the "good guys," relatively speaking, but they are more of the "moderate far right" mainstreaming party type, not the hardcore radical type supported here. Yes, indeed, "mainstreaming" can gain you a few more votes, but look how easy it is for the System to simply cancel an election with a bit of behind-the-scenes wheeling and dealing.
After all, the Swedish "center right" is likely confident they can swoop in and gather up those Sweden Democrat voters if they can wait long enough for those weak mainstreamed Sweden Democrat supporters to drift away and vote for "electable" conservatives. That's what you get from "mainstreaming" - the System still won't accept you, you are still a pariah, but on the other hand, a fraction of your support is a mile wide and an inch deep, and if you are perceived as not much different from "mainstream conservatives" (the whole point of "mainstreaming," eh?), then it is real easy for that inch deep support to melt away once the System frustrates the ability of your lukewarm supporters to cast an immediate vote for you.
What's needed are hardcore, disciplined supporters who would refrain from supporting the center-right, and thus demonstrate to "mainstream conservatives" that they have little to gain, politically speaking, from frustrating those farther to the right. Those conservatives may still act the same way, but at least you won't have the spectacle of them being rewarded with the votes of those they are frustrating.
Those who support "mainstreaming" are either too stupid to be useful or are actually enemies: either way, they need to be ridiculed and then ignored.