Workers' Party chief Low Thia Khiang dismissed criticisms of it being an arrogant party that does not uphold opposition unity.
Instead, he said the party believes the diversity in the "complex" opposition camp, with its different leaders and political beliefs, makes it inconceivable for unity to be achieved.
"If you try to force people of different characters together, you will not get bliss but may even lead to ugly fights," said Mr Low, speaking in Mandarin during the party's second rally last night.
"Such a scenario will only let people lose confidence in the opposition and become an impediment to Singapore's democratic development."
As its strength and numbers in Parliament grew, the Workers' Party (WP) has come under increasing fire from other opposition parties in recent years.
The attacks intensified in the lead-up to the Punggol East by-election over its refusal to negotiate, most notably with the Singapore Democratic Party (SDP).
Mr Low acknowledged the pressure, saying that he felt increasingly sandwiched between the People's Action Party (PAP) and other WP critics, especially those from the cyberspace.
But the party still wants to go it alone because it fears the history of opposition disintegration repeating. He pointed to how the opposition fell apart after the 1991 polls, when it produced four opposition MPs, including himself after a win in Hougang.
But a split within the SDP in 1993 between its then chief Chiam See Tong and protege Chee Soon Juan triggered a downward spiral for the opposition, leading to only Mr Chiam and Mr Low getting re-elected in 1997.
Thereafter, the party decided to stay independent even when several parties set up the Singapore Democratic Alliance.
But he stressed the WP is not arrogant nor disrespectful of others. Instead, its aim is to not disappoint Singaporeans hoping for a stronger political force to check on the PAP. "We're doing this so that we can continue to make a contribution to Singapore's democracy," he added.