Is this a wise strategy? I see two arguments countering each other. I suppose the one people agree with probably depends on their pre-existing views:
"this is a wise strategy. Other countries' parties attempts to emulate right-populist platforms did nothing to stem their rise and instead emboldened them. The SD's will have a natural ceiling in the population which locks them from power - it's best to not engage with them or legitimise until they fizzle out like, say, Vlaams Belang or the BNP did."
"This is not a wise strategy. Ignoring the populists' demands will enrage them and cause them to grow even more; while giving dissatisfied citizens an untested outlet to express their rage. An unchecked angry group of populists would cause chaos in both a parliamentary context (with SD's wrecking bills) and in an extraparliamentary sense".
That's of course one of the central questions asked by populism scholars across the world regarding the response of the mainstream to these upstarts. As you point out, some argue that moving to the right only gives the right-wing populists more legitimacy...i.e. it signals to potential voters of these parties that it's now ok to cast your ballot for them since their views are far from outlandish.
Some scholars have also found that right-wing populists only gain legitimacy if the entire party system shifts rightwards on a topic like immigration. If only the center-right alters its stance while everybody else remains liberal on the topic, right-wing populists fail to be able to capitalize on these moves. I suppose the recent DPP success could - according to this theory - be explained by the fact that the Social Democrats have also hardened their rhetoric on immigration.
Cas Mudde (probably the pre-eminent scholar on the topic) has tried to answer the question by incorporating the matter of "issue ownership" - meaning that if a right-wing populist party is seen as the natural go to choice on a given topic (such as immigration) then center-right parties are fighting a losing battle by moving to the right. All they're doing is politicizing an issue whose increased salience favors the populist right. If a right-wing party is primarily seen as a protest party on the other hand, other parties are able to move in and cut off the oxygen. I suppose the central question in Sweden now is what kind of party the SD are.
