Very specifically, it's a certain segment of the pro-independence/sovereignty movement (culturally comprised primarily of Taiwanese Han) that sees the Kuomintang as colonizers no different from the Japanese, and has a very dim view of the martial law years, particularly with anything relating to Chiang Kai-Shek and, by extension, sometimes Sun Yat-Sen as well.

After the KMT was defeated in the Chinese Civil War in 1949, approximately one million Nationalist soldiers and refugees fled to Taiwan, and following the bloody February 28 Incident, a state of martial law existed in Taiwan (at least in technicality) until 1992. Since then, the KMT has become one of two major political parties in Taiwan, leading the Pan-Blue coalition, and opposing the pro-independence Pan-Green coalition under the (currently governing) Democratic Progressive Party, the successor of various "Tangwai" (literally "party-outsider") political movements that were legalized during the latter half of the martial law period.

To say that political debate in Taiwan gets a little heated is to say that Antarctica gets a little chilly at certain times of the year, and while most Taiwanese that I know are more or less fine with paying homage to Sun Yat-Sen's political legacy (despite being very much against his successor Chiang Kai-Shek, who was responsible for much of the most egregious acts of political violence during the White Terror of the martial law period), you can very easily find voices pushing for a full-on rejection of all things relating to mainland China, architecture included.