I find "no pressure" comes off as less condescending.
"Only if you want to" heavily implies it's fully their decision and that you asking totally want your desired outcome. 

But it's also what word you add emphasis to for example

"ONLY if you want to" vs "only if YOU want to" or "only if you WANT to". 

I hope this makes sense. I grew up around a mother who took everything as the most negative context so I think a great deal about what I say and how.

In a social context, like 

"Can you tell me about \_?"

Perhaps some of it is because those refusals are often followed by "why not" or "why are you being prickly about it", but I'm curious if this is a sum of my subjective experience, or if it's the question construcion.

Why do questions followed by "Only if you want to" feel like there's pressure to accept?