Is it okay to not support Internet Explorer 6-8 and other legacy browser versions when designing a site? I asked this as it makes project completion time for websites very long.
It also forces the developer to juggle multiple targets in a single responsive design. Most themes we see in ThemeForest and co are built by team of developers and therefore are easily able to get there design to be all-round responsive. I like to hear the opinion of NairaLanders.

I'm not a programmer but I'd hit you with a response built over years of knowledge:
Go the way of big companies and design webpages only for trending browser versions. A minority of people still exist who use old browsers but their numbers make a negligible difference. Anyone on the internet visiting a site created in the past four -five years is likely using the most recent version of their internet browser.

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What about client who don't understand this fact and demand you support back to IE6-8? Lots of people still install windows Xp Pack II and tend to believe its default IE6 should work with any website.