LU, on the contrary. The extremists are doing the chillul Hashem. Opposing them is a kiddush Hashem.
Little, only selling “kosher” phones to Jewish customers would open him up to fines for discrimination. Moreover, halachically it is muttar mi manafshach. If smartphones are muttar (and I know at least one rav who has one) it is certainly muttar. Even if it is not, being that there are many gentiles who sell the phones it is only a question of
מסייע לדבר עבירה. This is allowed in a case where the aveira has not yet been committed ( Netziv, Responsa Meshiv Devar 2:31-32). Even more so being that it is not at all clear that the customers will go into inappropriate sites.